During the ongoing Russia–Ukraine war, the risks of nuclear weapon use or a nuclear accident at nuclear plants in Zaporizhzhia, occupied by Russia, and Kursk have been repeatedly highlighted. Russia has frequently threatened to use nuclear weapons, the latest instance being on February 24, 2026, when it accused the UK and France of helping Ukraine acquire nuclear capability and warned that such actions could trigger a confrontation between nuclear powers. Later, between 18 and 20 May 2026, Russia and Belarus conducted joint nuclear exercises involving missile units and strategic forces practicing nuclear weapon delivery and deployment. Such threats have emanated since the start of the conflict from various levels of the Russian government and military, including President Putin. Immediately after the invasion of Ukraine, Putin ordered Russia’s military on 27 February 2022 to put its deterrence forces, which include nuclear weapons, on “special alert.” On September 21 of the same year, he reiterated his threat to use all types of weapons, asserting that it was not a bluff. This clearly shows that his threats so far had not been taken seriously or lacked credibility, as they were driven by battlefield reversals and a shortage of military personnel in the invasion’s initial stages.

Russia’s nuclear threats reduced in 2023 when its military operations were achieving favourable results, another reason for their low credibility. However, nuclear rhetoric picked up again in 2024, including exercises simulating “theatre” or regional nuclear attacks, in contrast to “strategic” nuclear exercises simulating war with the US. Russian threats have been so frequent and unceasing that they no longer make headlines in Western media. Their recurrence has eroded credibility, rendering them ineffectual. These provocative articulations are assessed to be inconceivable, exaggerated, routine, discordant, and implausible.

The intent of these threats appears to be imposing restraint and influencing Western decisions. Russia has essentially reinforced two red lines for the West: first, the unacceptability of direct involvement and deployment of NATO boots on the ground in Ukraine; second, deterring and constraining the West from providing military aid to Ukraine, specifically offensive weapons platforms that could threaten Russian territory. In the first case, the US and NATO leaders have been extremely cautious and avoided direct resistance to Russia’s invasion. While military assistance was slow initially, it picked up gradually. The West has disregarded Russia’s warnings and provided Ukraine with weapon systems explicitly opposed by the Kremlin, including tanks, drones, and long-range missiles. On August 1, 2024, the first batch of long-awaited F-16 jets arrived in Ukraine, significantly bolstering its air force. Ukraine has since carried out aerial strikes deep into Russian territory, even hitting oil refineries in Siberia. Earlier, it forced Russia to scale down its Victory Day Parade on 9 May 2026 in Moscow due to security concerns. Despite its red lines being violated, Russia has avoided striking NATO territory. This reflects the continued effectiveness of strategic mutual nuclear deterrence among parties to the conflict.

Historically, the use of tactical nuclear weapons in Europe by either side has not been taken seriously. During the Cold War, NATO planning envisaged immediate use of hundreds of tactical nuclear weapons in response to a conventional Soviet attack in Europe, to hedge against conventional asymmetry. Yet, nobody assigned a high probability to this option. Similarly, the Soviets remained largely hostile to the idea that nuclear war could be fought in a highly limited manner, such as small-scale battlefield exchanges for bargaining purposes.

India does not face a major nuclear threat from large nuclear powers—the US and Russia—or the medium-sized nuclear forces maintained by the UK and France. Its major adversaries are China and Pakistan. China is the first and only nuclear weapon state recognized under the NPT to have maintained an official NFU policy continuously since it first acquired nuclear weapons in 1964. Since then, it has shown no proclivity for nuclear blackmail or coercive diplomacy based on nuclear threats. While a full-blown war initiated by China to resolve the boundary issue is unlikely in the short term, limited conflict due to escalation of local issues on the LAC could occur, as seen in Eastern Ladakh in 2020. As long as nuclear capabilities remain, China’s intentions can change at any time.

Pakistan’s case is entirely different. It considers the threat from India existential and inimical to its very idea of nationhood. Its strategic thought process is based on proactive and pre-emptive actions. Nuclear weapons give Pakistan the confidence to face a larger neighbour with asymmetry in military, economic, and industrial capacity. It professes that nuclear weapons reduce the probability of conventional conflict. Accordingly, it has a declaratory doctrine of “first use,” and lately has been advocating “early use” as part of strategic signalling to India. It has also alluded to ambiguous territorial, infrastructure, and economic red lines. Ambiguity and irrationality reinforce the deterrence value of nuclear threats. Pakistan seeks to deter India at all levels of war—nuclear, conventional, and sub-conventional—while denying India the same equation. It has regularly resorted to nuclear sabre-rattling in past conflicts to influence Indian decision-makers, as demonstrated during the Kargil War, Operation Parakram, surgical strikes across the LC, the Balakot air strikes, and recently Operation Sindoor.

In contrast, India’s nuclear doctrine is based on the twin pillars of NFU and minimum credible deterrence, resulting in massive retaliation in response to a nuclear attack. India believes that nuclear weapons deter only nuclear war and are of strategic relevance, not for warfighting. Suggestions have been made in recent years to revise the doctrine, abandon NFU, and incorporate “first use.” The main arguments advanced include the complex regional security environment and technological advances that may degrade the potency of a second strike.

Deterrence is widely accepted as a psychological construct rather than an end in itself. It should inspire fear, where the perceived cost of deterrence breakdown outweighs the benefits of war as a dispute resolution instrument. Even if a nation declares NFU, no one will trust that it will remain committed to NFU if its vital interests are at stake. A degree of calculated ambiguity in a nuclear doctrine is essential for credibility. Restraints on nuclear war are mainly intellectual, ethical, and doctrinal. During the Cold War, the USSR could not have invaded Western Europe even if the US had a declaratory NFU policy. Importantly, it is against the national interest of responsible and status quo powers like India to weaken the nuclear threshold. Conventional attacks are largely considered within the rules of international behaviour in a jus ad bellum situation, such as punitive conventional retaliation by India in response to high-profile terrorist incidents. The possibility of escalation or total eruption makes it unlikely that either side could achieve decisive victory in a limited war by using nuclear weapons.

Nevertheless, the existence of nuclear weapons cannot be downplayed, and they may be used in extreme cases by a nuclear-capable state. Threats to use nuclear weapons will continue to be made repeatedly to deter and influence adversary decision-making by playing mind games. Under the nuclear overhang, space for conventional operations exists, though its extent remains undefined and can be expanded by the side exercising escalation dominance. Moreover, deterrence is not static; it requires active escalation management throughout a crisis. Therefore, lessons from recent conflicts, particularly the Russia–Ukraine war, reinforce the enduring relevance, resilience, and credibility of India’s nuclear doctrine in maintaining strategic stability.

The post Nuclear Deterrence Stability in the Ukraine Conflict appeared first on IMR.

A variable-yield warhead (often called “dial-a-yield”) is engineered to allow selection of different explosive yields from the same device, granting military planners flexibility in deployment. Achieving this adjustability is a complex engineering challenge: it requires precise control over the physical processes in each stage of the warhead. The following discussion provides a technical overview of the warhead’s architecture and the mechanisms enabling yield modulation, including tritium boosting, spark plug and tamper design, material choices, and the use of advanced computational modeling. Insights from recent high-energy density experiments are also integrated to illustrate how modern research validates the underlying design principles.

Warhead Architecture: Primary and Secondary Stages

Primary Stage (Fission Trigger): The primary is a small implosion-type fission bomb that serves as the trigger for the secondary.  Typically composed of a core of fissile material (plutonium-239 with possibly uranium-235), the core is surrounded by chemical high explosives and a neutron-reflecting tamper or casing.  Modern primaries are almost universally boosted fission devices: a mixture of deuterium-tritium (D-T) gas is injected into the hollow core of the fissile pit just before detonation. When the high explosives compress the core, the fission chain reaction heat and pressure cause the D-T gas to undergo fusion, releasing a burst of high-energy neutrons. These fusion neutrons dramatically accelerate the fission chain reaction, allowing a much larger fraction of the fissile material to fission before the core disassembles. In effect, boosting can nearly double the fission yield by fissioning more fuel, since the 14 MeV fusion neutrons are far more likely to induce fission than the neutrons from unboosted fission alone. Boosting not only increases yield but also permits smaller primary designs that are “efficient” (more of the fissile core is burned) and immune to pre-detonation. In fact, the technique is so effective that essentially every modern nuclear weapon uses a boosted primary design. The primary’s yield can range from a few kilotons upward, and in a variable-yield system this output is made adjustable (as discussed in a later section) by controlling factors like tritium injection and neutron initiation timing.

Secondary Stage (Thermonuclear Assembly): The secondary is a physically separate component that contains the fusion fuel and other elements necessary for a thermonuclear reaction. In a classic Teller-Ulam layout, the secondary comprises a cylinder of fusion fuel (often lithium-6 deuteride salt, a dry solid) packed around a central spark plug of fissile material (usually a rod of plutonium-239 or uranium-235). This assembly is enclosed by a heavy tamper/pusher, commonly made of depleted uranium or tungsten, which serves dual roles: confining the fuel during compression and, if made of fissionable material like U-238, contributing additional yield via fast fission. The secondary is housed at the opposite end of the warhead casing from the primary, separated by an empty radiation channel (often filled with low-density plastic foam) and sometimes a dense shield or interstage to prevent premature energy transfer. When the primary detonates, a flood of soft X-rays is released and reflected within the sealed weapon casing (the “radiation case”). These X-rays rapidly fill the radiation channel and symmetrically ablate the outer surface of the secondary’s tamper. The ablation acts like a rocket exhaust, driving the tamper and the fuel capsule inward. This radiation-driven implosion crushes the secondary to very high densities. As the secondary is compressed, the central spark plug is also compressed and heated; it soon reaches criticality and undergoes its own fission burst. The spark plug’s fission energy further heats the surrounding fusion fuel, helping to ignite thermonuclear burning in the dense lithium deuteride material. In the ensuing microseconds, fusion reactions spread through the secondary, producing a flood of 14 MeV neutrons and releasing enormous energy. The lithium-6 deuteride is designed such that when bombarded by these neutrons, it breeds tritium in situ (via Li-6 + n → T + He reactions), providing fresh tritium to sustain fusion burn – a process sometimes termed the “jetter” cycle. The combination of X-ray implosion, spark plug fission, and on-the-fly fuel breeding enables the secondary to contribute yields in the hundreds of kilotons to megaton range. Notably, the heavy tamper around the fusion fuel greatly increases overall yield: the secondary’s fusion neutron output induces fast fission in a U-238 tamper and casing, which can account for the majority of the weapon’s total yield. (In typical U.S. thermonuclear weapons, over 80% of the yield comes from fission of the U-238 parts.) This tamper fission greatly amplifies yield but also increases residual radioactive fallout. In some designs, alternate tamper materials (like lead or tungsten) have been tested to produce “cleaner” explosions with a higher fraction of fusion energy at the cost of lower total yield.

Mechanisms for Variable Yield Control

Engineering a variable-yield warhead means the device can be reliably configured to produce different yield outputs on command, typically through pre-detonation settings. Several design mechanisms enable this adjustability:

•  Tritium Boost Gas Regulation: The primary stage’s yield can be tuned by adjusting the amount of tritium-deuterium gas injected into the pit. A full D-T fill maximizes boosting (and thus fission yield), whereas a partial fill or no fill yields a much lower primary output. By calibrating the boost gas pressure or quantity to discrete levels (for example, 0%, 50%, or 100% of the standard charge), engineers can define preset yield levels for the primary. In practice, a tritium reservoir system and metering valve are used to introduce the desired amount of gas just milliseconds before detonation. At full boost the primary might yield on the order of a couple hundred kilotons, whereas with minimal or no boost it might only yield tens of kilotons – a dramatic difference arising from the presence or absence of those extra fusion neutrons that drive the fission reaction to completion. Tritium, with its 12.3-year half-life, must be replenished periodically in the warhead’s reservoir as part of routine maintenance, but this is an accepted trade-off for yield flexibility. By precisely controlling boost gas fill, modern warheads effectively have a built-in “dial” for the primary yield.

•  Neutron Initiator Timing: Beyond boosting, another lever on the primary’s yield is the timing of the External Neutron Initiator (ENI). All modern implosion primaries include a neutron source that injects a burst of neutrons at the moment of maximum compression to ensure a prompt chain reaction. By deliberately adjusting when this neutron pulse is introduced, the efficiency of the fission burn can be modulated. If the initiator fires slightly early (just before optimal compression), some fission will start when the core density is lower than ideal, thus delivering a reduced yield because the core will blow itself apart before burning completely. In contrast, firing at the optimal peak compression yields the maximum fission output. Therefore, by designing the detonator firing circuit to introduce a small, controlled delay or lead in the neutron injection, one can throttle the yield downward in a repeatable way. For instance, an “early” initiator pulse might intentionally produce a partial fizzle (lower yield), whereas the normal pulse timing produces full yield. This method provides a fine, electronic control of yield just before detonation. It requires a precision timing system for the pulsed neutron source (such as a pulsed plasma discharge or a miniature accelerator-driven D-T source) but allows adjustments in yield without any mechanical changes to the device.

• Secondary Stage Engagement (Selective Ignition): The largest jump in yield comes from whether the secondary stage is ignited or not. A variable-yield warhead can be designed to essentially turn off the secondary in low-yield mode, so that only the primary detonates. There are a few engineering approaches to achieve this. One straightforward method is to exploit the primary’s yield threshold: if the primary’s yield is kept below a certain level (by using the above techniques), the X-ray energy may be insufficient to compress and ignite the secondary. In that scenario, the secondary fails to detonate and the total yield is just the primary’s output – drastically lower than the full design yield. However, solely relying on a reduced primary may be unreliable if, say, a higher setting accidentally triggers the secondary. Thus, more direct secondary inhibition mechanisms have been theorized. For example, a system of movable high-Z shutters or curtains within the radiation case can be used to partially block or absorb the primary’s X-rays in low-yield mode. In a high-yield setting these shutters retract, allowing full radiation coupling, but in a low-yield setting they insert into the line-of-sight between the primary and secondary, protecting the secondary from compression. Such an arrangement would likely use tungsten or uranium sliding panels, and would need ultrafast actuators (as the time between primary and secondary detonation is on the order of microseconds). In practice, implementing moving parts in a warhead is challenging, so designers might opt for passive methods – for instance, a variable-density filler in the radiation channel that either absorbs more radiation in one configuration or becomes transparent in another. Another approach is the use of a small auxiliary explosive to pre-disrupt the secondary in low-yield mode (for example, jostling the fusion fuel so it won’t compress properly), though this is largely speculative. Regardless of method, the goal is to have confidence that in “primary-only” mode the secondary remains truly inert. If successful, this gives a warhead two very distinct yield tiers: a lower-tier (e.g. tens of kilotons or less) from the primary alone, and an upper-tier (hundreds of kilotons to megaton) when the secondary is engaged. Designing the secondary to reliably fail safe when needed – without compromising its performance when enabled – is a significant engineering challenge in variable-yield systems.

• Tamper and Spark Plug Configuration: Certain design choices in the secondary can also modulate yield outcomes, though these are set during design rather than adjusted in real time. The tamper material, as noted, has a profound effect on total yield. Using a uranium-238 tamper maximizes yield by contributing additional fission (fast neutrons from the fusion stage will fission the tamper and casing, adding to yield). In contrast, a non-fissile tamper (such as one made primarily of lead or tungsten) would yield a much lower total explosive energy for the same primary and secondary, since the fusion stage’s neutrons do not generate extra fission explosions in the tamper. This was demonstrated in certain test devices historically dubbed “clean bombs” which sacrificed yield for reduced fallout. While tamper material isn’t a field-adjustable setting, warhead designers consider it as a way to tailor a weapon’s nominal yield and fallout characteristics to mission requirements. The spark plug is another design element influencing yield: a larger or more enriched spark plug will produce a stronger initial fission spike inside the secondary, ensuring the fusion fuel ignites more completely (thus raising yield). If the spark plug is omitted or made of very low mass, the secondary might not ignite at all without it, or would burn less efficiently. Essentially, the spark plug provides an on-demand energy injection to kick-start fusion in the secondary. All modern high-yield secondaries include a spark plug to guarantee ignition; however, if one wanted a design that could alternate between a high fusion yield and a mostly fission-only yield, one could hypothetically include a mechanism to disable the spark plug in low-yield mode (for example, by not allowing it to compress fully or by blocking the neutrons that would initiate it). In practice, such fine control is extremely difficult, so the spark plug’s role is more about ensuring the secondary ignites robustly in normal operation. Nonetheless, its presence and design set the fundamental upper limit of the secondary’s output. Together, choices in tamper and spark plug configuration establish the device’s maximum yield potential and the division between fission and fusion contributions, which are key factors in any variable-yield design strategy.

Materials and Design Considerations

The performance of each stage and the range of yields attainable are tightly linked to material selection and engineering of the components:

• Fissile Core: Most variable-yield warheads use plutonium in the primary core (often alloyed with gallium for phase stability). Plutonium’s high density and fast fission kinetics allow for a compact pit that can achieve high compression and reactivity, which is advantageous for achieving reliable ignition especially in lower-yield (less boosted) configurations. Highly enriched uranium can be used as well or in composite pits, but plutonium’s properties make it preferable for smaller, efficient primaries. The core is surrounded by a reflector/tamper (beryllium or natural uranium) that serves to reflect neutrons back into the core and tamp the explosion’s expansion momentarily. This not only increases yield efficiency but also aids in maintaining chain reaction conditions when yield is being throttled (e.g., in a low-boost setting, a good reflector ensures even the reduced neutron population is utilized). In variable-yield applications, the core and reflector materials must perform consistently across the range of compression and boost scenarios – a significant consideration in design validation.

•  Fusion Fuel: The secondary’s fusion fuel is typically lithium-6 deuteride, chosen for its stability and high energy density. Li-6 deuteride is a solid at room temperature, making it convenient to machine into a desired shape (often a cylinder or sphere) and it can be enriched in lithium-6 to optimize tritium production. When the secondary is imploded and heated, neutrons from either the primary or the spark plug convert Li-6 into tritium, which then readily fuses with deuterium. This material choice obviates the need to physically preload large quantities of tritium in the secondary (which would slowly decay and also pose handling issues). Instead, the fusion fuel breeds its own tritium in the instant of detonation. The downside is that lithium deuteride requires extremely high compression and temperature to burn efficiently – hence the need for the robust implosion and spark plug. In warhead design, the exact composition (ratio of Li-6 to Li-7, and presence of any deuterium-tritium gas boost in the secondary) can be tuned to alter performance. For example, adding a bit of D-T gas in void spaces of the secondary can help “pre-seed” the fusion reaction for more yield, but at the cost of complexity and more rapid yield decay due to tritium half-life. Generally, Li-6 deuteride has been the standard for decades due to its reliability and predictable behavior under extreme conditions.

• Tamper and Case Materials: As discussed, using a depleted uranium tamper around the secondary maximizes explosive yield by leveraging fast fission. The weapon’s outer case is also often made of stainless steel or an alloyed uranium (for weight and strength) and serves as the radiation case that traps the X-rays for the microseconds needed to drive the secondary’s implosion. In variable-yield warheads, if designers included physical devices like shutters, these would likely be made of a high atomic number metal (tungsten or uranium) to effectively absorb or block X-rays when engaged. All materials in the secondary must withstand the primary’s initial shock and preheat without degrading so much that they fail to function in high-yield mode. Selecting materials thus involves balancing density (for inertia and tampering effect), opacity to radiation, and melting/vaporization thresholds. In some design studies, advanced materials like aerogels or specialized foams have been considered for the radiation channel filler to tailor how energy is delivered to the secondary. These materials can be engineered to either transmit or absorb radiation more in one mode or another, hence contributing to yield control. Material choices are validated through sub-scale experiments and extensive simulations to ensure they perform as expected in both minimum and maximum yield configurations.

•  Precision Engineering: A variable-yield device introduces additional hardware that must function flawlessly under nuclear detonation conditions. For instance, metering the tritium boost gas requires miniaturized high-speed valves that operate in the last moments before the explosive fires. Timing circuits for neutron initiators must be hardened and extremely precise (nanosecond-scale) to achieve the desired yield dial-down without risking a dud or runaway yield. If mechanical interlocks (like shutters or sub-stage barriers) are employed, they need to survive the acceleration and extreme environment until the moment they operate. All components – conventional explosives, detonators, wiring, safety mechanisms – must be engineered with tighter tolerances because the margin for error is smaller when attempting to modulate yield. The warhead must also be robust across the full yield range: it should not accidentally produce more than the intended yield in the “low” setting nor fail to achieve full yield in the “high” setting. Achieving this reliability is a foremost engineering concern, influencing everything from the explosive lens design (shaping the implosion for different yields) to the placement of sensors or monitors that ensure the device is performing as configured.

Computational Modeling and Validation

Because full-scale nuclear testing is limited, designers rely on sophisticated computational simulations to validate that a variable-yield warhead will perform as intended across its settings. Modern nuclear weapon design codes are massive hydrodynamics and radiation transport simulations that model the device’s behavior from the millisecond of high-explosive detonation through the nanoseconds of nuclear reactions. These codes incorporate detailed physics: shock compression of materials, fission chain reactions (with neutron transport), fusion burn kinetics, radiation flow, and even secondary effects like fuel-tamper mixing. To handle variable yields, simulations are run for multiple scenarios – e.g. a full-yield case and a low-yield case – to ensure both meet design predictions. Typically, designers start with lower-dimensional models: a one-dimensional spherical simulation can approximate the primary’s implosion and help calibrate how much boost gas yields what output, by comparison to past test data or known device benchmarks. Likewise, a simplified 1D or 2D model of the secondary (with an assumed X-ray drive) is used to check whether it will ignite or not under certain input energies. These sub-component models allow rapid iteration and “tuning” of design parameters (such as adjusting the thickness of a tamper or the timing of an initiator) before committing to a full-up simulation.

The final verification involves full 2D or 3D simulations of the entire warhead. Two-dimensional (axially symmetric) simulations are a workhorse for warhead design, as they can capture the primary-to-secondary energy coupling along the weapon’s axis and some asymmetry effects, while still being computationally feasible. Three-dimensional simulations offer the most fidelity, allowing analysts to probe off-axis phenomena or manufacturing imperfections (e.g. how a slight asymmetry in the high explosives or a gap in insulation might affect yield). However, 3D runs are exceedingly demanding in compute time, especially for a multi-megaton-yield device. Thus, a handful of high-resolution 3D simulations might be used to validate that no unexpected behavior (like an inadvertent partial secondary ignition in “off” mode) occurs, whereas many 2D runs map out the performance envelope. Computational validation focuses not just on nominal performance but also on edge cases: for example, ensuring that an accidental one-point initiation of the primary’s high explosive will not produce a significant nuclear yield (a safety requirement), or that the weapon will not detonate if dropped or exposed to a fire. For a variable-yield warhead, simulations also explore the transition points – i.e., the exact primary yield at which the secondary lights up. This is critical for confidence that the secondary can indeed be reliably suppressed. The outcome of these extensive simulations is a predicted yield range (for instance, a low setting of ~0.5 kilotons and a high setting of ~50 kilotons for a tactical warhead, or 10 kt vs 100 kt, etc., depending on design) with associated uncertainties. Engineers use uncertainty quantification techniques to put error bars on these yields, by varying input parameters within their plausible ranges and observing the effect on output. If the uncertainty overlaps between the “low” and “high” yields (an indication the settings are not distinct enough), the design must be revised for a clearer separation. Often, historical nuclear test data and experiments are used to calibrate these codes – for instance, data from past boost efficiency trials or from the single-stage detonation of secondary materials. Through this modeling-and-simulation-driven process, the warhead design is refined until it consistently meets its yield specifications. Only then would it be considered for engineering development, and even then, sub-critical experiments or laboratory tests might be done on certain components (like imploding surrogate materials with high explosives) to gather real data to confirm the simulations.

Insights from recent experiments

In recent years, high-energy-density physics experiments have provided critical insights reinforcing confidence in the fundamental physics underlying thermonuclear warhead designs. Recently, the National Ignition Facility (NIF) in the United States achieved a significant milestone by generating more fusion energy than the energy input from lasers, demonstrating a clear transition to self-sustaining fusion reactions. In this experiment, fusion-produced alpha particles (helium nuclei) deposited their energy locally, causing substantial reheating of the surrounding hohlraum cavity-significantly increasing its radiation temperature within fractions of a nanosecond. This observed phenomenon, wherein fusion-generated energy feedback stimulates further fusion, experimentally confirms the long-theorized concept of alpha particle self-heating. Such alpha-driven self-heating underpins the fundamental physics of the secondary stage in thermonuclear warheads, enabling a rapid escalation from initial ignition to full-scale fusion burn. These experiments align closely with theoretical yield-scaling models that describe the highly non-linear growth of fusion output once alpha heating becomes significant, validating computational approaches crucial for predicting warhead performance. Although the laboratory conditions are not identical to operational environments, these high-yield experiments nonetheless provide essential validation data, enhancing confidence in computational models used to design and predict the behavior of variable-yield warheads. Ultimately, such insights support precise control over warhead yields, allowing reliable adjustments between ignition states-a core requirement for advanced strategic weapon systems.

Conclusion

The development of a variable-yield thermonuclear warhead is a tour-de-force of modern engineering and physics. By carefully architecting the primary and secondary stages and incorporating mechanisms for yield control – from tritium boosting systems and precision neutron timing to potential secondary isolation techniques – designers can create a single weapon system that fulfills multiple roles. Each adjustable element, however, introduces complexity that must be mastered through rigorous design, material science, and simulation. The warhead’s architecture (primary trigger, fusion secondary with spark plug and tamper) provides the foundational framework, and on top of this, engineers overlay control features that modulate the energy release. Cutting-edge computational modeling, honed by decades of test data and enhanced by new experimental results, underpins the validation of these designs without full-scale detonations. The result is a weapon whose yield can be tailored to tactical or strategic objectives while ensuring safety and reliability. In essence, the variable-yield warhead represents the convergence of classic nuclear design principles with innovative engineering solutions – all aimed at managing the incredible energies of a thermonuclear explosion with precision and confidence.

Kartikeya Sethi is the Founder of Vel Atomics

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Pakistan’s Khushab nuclear complex, located in Punjab province, sits at the heart of the country’s weapons-grade plutonium production effort. This facility stands apart from standard nuclear power plants, thanks to its specialized heavy-water-moderated reactors – four in total – that collectively produce significant amounts of both plutonium and tritium, two essential ingredients for modern nuclear weapon designs. Estimates suggest that Pakistan currently maintains a stockpile of around 170 nuclear devices, each requiring on the order of 10 grams of tritium to achieve boosted fission yields. By leveraging short irradiation cycles, uranium metal fuels, and potentially lithium-6 doping, these reactors can generate not only the desired high-purity ²³⁹Pu (weapons-grade plutonium) but also tritium-albeit at levels that may be constrained by operational inefficiencies.

A pivotal enabler in this setup is heavy water (D₂O), produced onsite using hydrogen sulfide (H²S) exchange technology. Heavy water allows the use of natural or low-enriched uranium, making the process more flexible and cost-effective for weapons purposes. Additionally, these reactors can be tuned to shorter burnups – around 5-6 MWd/kg – to keep the plutonium at ²³⁹Pu 90 wt%. Tritium emerges from two main pathways: neutron capture in deuterium (within the D₂O) and irradiation of lithium-6 (either in targets or doped into reactor elements). Because tritium decays at a rate of 5.6% per year, Pakistan must replenish its stockpile constantly to keep existing warheads operational, which, in turn, shapes how Khushab’s reactors might be run-whether in single-batch modes or partial/ continuous recycling to maximize throughput of weapons-usable materials.

This article:
1. Examines the Khushab Reactors’ Design and Operation
•              Outlining the four heavy-water reactors, their typical power ranges, and why short-cycle irradiation is crucial for achieving weapons-grade plutonium.
•              Highlighting the importance of uranium metal fuel and describe how its properties facilitate rapid breed-out of ²³⁹Pu .
2.            Explore Heavy-Water Production and Lithium-6 Doping
•              Detailing the hydrogen sulfide exchange process that supplies Khushab’s heavy water.
•              Explaining the use of lithium-6 targets or doping, illustrating how tritium is generated in tandem with plutonium.
3.            Analyzing Tritium Requirements for an Arsenal of 170 Devices
•              Demonstrating how tritium’s half-life drives annual replenishment needs for existing warheads.
•              Presenting a more realistic tritium production range (down 30-35% from theoretical maxima) and show how this impacts the number of additional weapons each year.
4.            Quantify the Potential for New Warhead Production
•              By comparing the available plutonium output and the leftover tritium to calculate 3-5 new boosted devices per annum.
•              Discussing how short reactor cycles, frequent refueling, or partial reloads can amplify or constrain these figures.

By piecing together these reactor operations, fuel cycles, and radioactive by-products, we gain a clearer view of how Pakistan sustains and potentially expands its nuclear arsenal. The Khushab complex emerges as a technically sophisticated enterprise that, through judicious use of heavy water, uranium metal fuel, and lithium doping, can co-produce high-quality plutonium and tritium. Understanding these processes, along with the numbers that shape arsenal maintenance and growth, remains central to grasping the full scope of Pakistan’s nuclear posture.

ALSO READ: Pakistan Army rubbishes Imran Khan allegations; says nukes are safe

Operational Layout: Three Modes of Khushab Reactor Operations
One of the distinctive features of the Khushab heavy-water reactors is their flexibility in how they can be fueled and operated. Depending on Pakistan’s objectives-tritium production for boosting to maximizing weapons grade Plutonium production-each reactor can be run in a specific mode. These modes differ in terms of fuel cycle length, lithium-6 doping, and burnup levels. Below is an outline of the three principal modes:

1. Baseline “Clean Core” Mode
Objective: Higher burnup for somewhat more conventional operations, not aimed at producing weapons-grade plutonium.
A.            Fuel & Burnup
•              Typically uses low-enriched uranium (could be 3.5-4% ²³⁵U) or even natural uranium, depending on design.
•              Operates with longer irradiation cycles (e.g.12-18 months, analogous to some commercial or research reactors) to extract more energy per kilogram of fuel.
•              The resulting plutonium has a higher concentration of ²⁴⁰Pu and other heavier isotopes (e.g. ²⁴¹Pu), making it unsuitable for weapons-grade needs.
B.            Tritium Production
•              Primarily from neutron capture in deuterium within the heavy-water moderator; lithium doping is minimal or absent.
•              Yields moderate amounts of tritium-tied to total neutron flux and operational conditions-but significantly less than a dedicated tritium-focused cycle.
C.            Fuel Recycling
•              Often a once-through approach or partial reload for experimental or civilian use.
•              This mode is not optimized for short discharge or high Li doping, so the impetus for reprocessing for weapons material is low.
Outcome:
•              A “clean core” yields relatively higher burnup but non-weapons-grade plutonium.
•              Tritium production is secondary, mostly a side effect of heavy-water usage, rather than a targeted outcome.

2.            “Tritium Core” Mode
Objective: Maximize tritium output-especially if the goal is to build or maintain boosted fission devices.
A.            Fuel & Li-6 Doping
•              The reactor can still use standard or lightly enriched uranium.
•              Lithium-6 doping (via targets) is significantly increased, so a greater fraction of neutrons produce ³H  (tritium).
B.            Cycle Length & Burnup
•              Can vary: some operators maintain a moderate cycle to strike a balance between tritium generation and overall reactor output.
•              Plutonium is still produced but has higher isotopic contamination (more ²⁴⁰Pu, ²⁴¹Pu  ) because the fuel remains in the core longer.
C.            Tritium Handling
•              Larger emphasis on tritium recovery and purification (through dedicated tritium extraction systems).
•              If the moderator or coolant is heavily doped with Li-6, specialized facilities are needed to capture the tritium.
Outcome:
•              High tritium yield due to lithium captures, but plutonium is not weapons-grade (longer irradiation times degrade the ²³⁹Pu  purity).
•              Useful when the operator’s main concern is sustaining or expanding tritium stockpiles.

3.            “Co-Production Core” Mode
Objective: Simultaneously produce weapons-grade plutonium (90% ²³⁹Pu) and significant tritium in one cycle.
A.            Short Irradiation for Pu
•              The fuel (often uranium metal for efficient breeding and short residence) is discharged at low burnup (e.g., 5-6 MWd/kg).
•              This ensures the plutonium remains high in   ²³⁹Pu content, avoiding excessive ²⁴⁰Pu  buildup.
B.            Enhanced Li-6 Doping
•              To drive up tritium production, operators may incorporate additional Li-6.
•              Each short cycle yields a batch of both high-purity plutonium and a notable quantity of tritium (recovered post-irradiation).
C.            Frequent Refueling / Partial Reload
•              Because burnup is capped so low, the reactor must be refueled more often (possibly every few months).
•              This leads to frequent shutdowns or continuous on-power refueling (if the reactor design allows).
•              Spent fuel is quickly reprocessed to extract the newly bred ²³⁹Pu .
Outcome:
•              Achieves both nuclear weapons materials in a single reactor cycle.
•              Less efficient in terms of energy production (since the fuel is discharged prematurely).
•              Typically the best approach for maximizing warhead potential:  90% ²³⁹Pu  plus tens of grams to over a hundred grams of tritium per year (depending on the reactor size and doping).

ALSO READ: NUCLEAR WEAPONS: Nuclear Dynamics in South Asia

How These Modes Impact Khushab’s Output
A.            Mode Selection is Driven by Objectives
•              Pakistan can switch between or balance these modes across its four Khushab reactors, depending on whether it prioritizes straightforward electricity/research (clean core), high tritium (tritium core), or co-producing tritium and weapons-grade plutonium (co-production core).
•              In practice, open-source assessments suggest co-production might be favored if the goal is to maintain a steady stream of both quality plutonium and sufficient tritium.
B.            Material Throughput
•              For co-production or tritium-focused modes, the reactors see frequent short cycles  -> more fresh or recycled fuel required.
•              Single-batch or partial reload patterns ensure ²³⁹Pu is extracted before significant neutron capture forms unwanted isotopes (²⁴⁰Pu, etc.).
C.            Arsenal Growth
•              Recent estimates place Pakistan’s arsenal at 170 nuclear devices.
•              If co-production is pursued, each Khushab reactor can yield a certain fraction of the required plutonium plus tens of grams of tritium per year, enough to maintain existing warheads (due to tritium decay) and produce 3-5 new devices annually in aggregate-depending on operational efficiency and doping strategies.

By adjusting among these three modes, Khushab’s operators effectively control the balance of weapons-grade plutonium, tritium yield, and overall burnup. This operational flexibility is what makes the Khushab complex central to Pakistan’s nuclear weapons program-allowing shifts in strategy as material needs evolve.

Tritium Requirements and Warhead Production Potential
An integral part of Pakistan’s nuclear weapons program revolves around managing tritium ³H – a short-lived isotope essential to boost the yield of fission warheads. Because tritium decays relatively quickly, maintaining and expanding a tritium stockpile becomes a continuous operational concern. This section explores how Pakistan’s estimated arsenal of 170 devices might drive ongoing tritium needs and how Khushab’s production fits into meeting those demands while still enabling the manufacture of new warheads.
A.            Existing Arsenal: Decay and Annual Replenishment
•              Tritium has a half-life of 12.32 years, meaning it decays at about 5.6% per year. Consequently, each device loses a fraction of its original T load annually.
B.            Annual Top-Up Needs
•              Each device’s 10 g T inventory diminishes by around 0.56 g per year (5.6% of 10 g).
•              Multiplied by 170 devices, the entire arsenal loses an estimated 95 grams of T annually.
•              Replacing that 95 g is necessary to keep the boosted warheads at full potency.
C.            Role of Purity
•              It is crucial that only high-purity tritium-free of contaminants-is used in warheads.
•              Because tritium often needs re-extraction and purification, Pakistan’s actual annual requirement may be somewhat higher than 95 g to account for processing losses.

Tritium Production at Khushab
A.            Reduced Output Estimates
•              Under ideal “co-production” mode, open-source estimates once placed the four Khushab reactors’ total tritium capacity near 200 g per year.
•              However, factoring in operational inefficiencies (maintenance downtime, suboptimal lithium doping, partial cycles), a 30-35% reduction is realistic.
•              This lowers the annual production to around 130-140 g across all four reactors.
B.            Meeting the Arsenal’s Replenishment
•              If Khushab provides  130-140 g T per year, then 95 g must go to replace decayed tritium in existing warheads.
•              That leaves  35-45 g surplus T for expansion or other strategic reserves.
C.            Tritium Extraction & Handling
•              Whether produced via lithium-6 doping (in metallic Li targets or Li-bearing coolant) or as a by-product of heavy-water operation, tritium must be removed from reactor systems.
•              Dedicated tritium recovery facilities (and possibly enrichment systems) are needed to purify T to weapons-grade quality.
•              This adds complexity and expense but is essential for ensuring a reliable supply of boost-quality tritium.

Plutonium and the Production of New Warheads
A.            Plutonium Availability
•              Short burnups (5-6 MWd/kg) at Khushab produce weapons-grade plutonium with  90 wt%  ²³⁹Pu.
•              Aggregate annual output from the four reactors can reach tens of kilograms of Pu-enough for several warheads if each requires 5-8 kg.
B.            Tritium-Driven Bottleneck
•              Even if plutonium is plentiful, tritium often becomes the limiting factor for assembling new boosted warheads.
•              With an estimated 35-45g leftover per year (after replenishing the existing stockpile), the amount of new weapons possible depends on each warhead’s T load.
C.            3-5 New Devices per Year
•              A typical boosted device might again use 10 g of tritium.
•              Given 35-45g of surplus, 3-4 new warheads per year are comfortably supported.
•              Some slight year-to-year variance (e.g., improved Li-6 doping or improved reactor uptime) might push this figure to 5 in especially productive periods.

Through these interwoven processes, Khushab’s reactors uphold Pakistan’s capacity to maintain an existing arsenal of 170 devices, each reliant on regular tritium top-ups, while still enabling an incremental growth in warhead count of 3-5 new boosted devices per year. The precise output each year hinges on reactor uptime, doping strategies, and reprocessing throughput-but in broad terms, this arrangement presents a robust pathway to sustaining and modestly expanding a plutonium-based, boosted weapon program.

Technical Underpinnings: Uranium Metal Fuel, Heavy Water Production, and Lithium-6
The Khushab reactors derive their unique dual-production capability-of weapons-grade plutonium and tritium-from a combination of fuel choices, moderator technology, and isotopic doping. This section delves deeper into these critical elements, explaining why uranium metal is chosen over typical uranium oxide, how heavy water is produced and utilized, and the significance of lithium-6 in enhancing tritium yields.
1.            Uranium Metal Fuel
a.            Why Metal Fuel Instead of Oxide
•              Higher Density: Uranium metal has a greater density of fissile atoms compared to uranium oxide (UO₂), which can favor faster conversion of ²³⁸Pu into ²³⁹Pu.
•              Rapid Neutron Economy: Short-cycle or low-burnup reactors benefit from a more reactive core at startup. Metal fuel offers improved thermophysical properties (higher thermal conductivity, more favorable neutronics) for breeding.
•              Easier Fuel Fabrication for Weapons-Grade Goals: When the objective is to discharge fuel early (at 5-6 MWd/kg) to preserve a high fraction of ²³⁹Pu, metal fuel rods can be replaced more readily without the complexities associated with longer-burnup oxide fuels.
b.            Drawbacks and Handling
•              Corrosion Sensitivity: Uranium metal can be more reactive with coolants and requires protective cladding (e.g., Zircaloy or stainless steel).
•              Higher Fabrication Cost: Producing and shaping metal fuel assemblies is more specialized than standard reactor-grade UO₂.
•              Weapons-Focused: The tradeoff is that metal fuel is far less efficient for electrical power generation at high burnups but is excellent for short, intense plutonium production cycles.
2. Heavy Water (D₂O) Production at Khushab
a.            Role of Heavy Water
•              Key Moderator: D₂O has a low neutron absorption cross section, making it ideal for fueling with natural or slightly enriched uranium.
•              Higher Conversion Ratio: The superior neutron economy means more neutrons survive to convert ²³⁸Pu  into ²³⁹Pu.
•              Tritium By-Product: As neutrons interact with deuterium nuclei, a fraction of them form tritium (3H), especially over multiple reactor cycles.
b.            Hydrogen Sulfide (H₂S) Exchange Process
•              Industrial Setup: Pakistan relies on exchange towers where chemical equilibrium between hydrogen sulfide gas and liquid water progressively enriches deuterium.
•              Scalability: Multiple units and large volumes of H₂S allow for a steady throughput of deuterium, eventually yielding high-purity heavy water.
•              Onsite Integration: The Khushab site is believed to have its own heavy-water production facility, ensuring a domestic, uninterrupted supply crucial for fueling short cycles repeatedly.
c.             Moderator Management
•              In specialized “tritium core” or “co-production core” modes, operators may carefully monitor D₂O purity (removing contaminants, including the trace buildup of tritium) to maintain the moderator’s reactivity while also recovering the tritium.
3. Lithium-6 for Tritium Enhancement
a.            Capture Reaction
•              ⁶Li+n→α+³H: Lithium-6 has a high cross section for thermal neutrons, making it a potent driver for tritium production.
•              Metallic Targets or Coolant Doping: Li-bearing targets can massively boost T output. This approach is especially favored if the reactor runs in a “tritium” or “co-production” mode.
b.            Facility Requirements
•              Tritium Recovery: Post-irradiation, the tritium must be extracted-either from the coolant or from discrete target elements. This process demands specialized handling and radiochemical processing to achieve the high purity needed for weapons usage.
•              Cost & Complexity: Lithium doping adds extra costs and engineering overhead, but it allows operators to meet the arsenal’s T needs (both for replacing decayed tritium in existing warheads and for fueling new devices).
c.             Synergy with Heavy Water
•              While D₂O alone can produce some tritium via, ²H + n → ³H adding Li-6 significantly increases total tritium yield.
•              This synergy is pivotal in the “co-production” mode, ensuring there is enough T to match the volume of newly produced weapons-grade plutonium.

In essence, Khushab’s choice of uranium metal fuel, reliance on onsite heavy-water production, and selective use of lithium-6 doping are tightly interwoven strategies. They maximize plutonium quality and tritium yields, ensuring that Pakistan can both sustain its arsenal of 170 boosted devices over time and incrementally expand it by an estimated 3-5 new warheads per year in a “co-production” operational regime.

Spent Fuel Reprocessing and Fuel Cycle Management
While the Khushab reactors themselves lie at the core of Pakistan’s weapons-material generation, reprocessing of the discharged fuel is what ultimately unlocks the produced plutonium. In parallel, specialized tritium extraction processes ensure that any ³H generated-whether via lithium-6 targets or the heavy-water moderator-is recovered at sufficient purity for weaponization. This section explains how spent fuel reprocessing undergirds the entire cycle, from short core irradiation to final warhead production.
A.            Why Reprocessing Is Crucial
a.            Extracting Weapons-Grade Plutonium
•              When fuel is discharged at 5-6MWd/kg burnup, the newly formed ²³⁹Pu still resides within a matrix of other isotopes, fission products, and unburned uranium.
•              Chemical separation is necessary to isolate plutonium from this highly radioactive mix.
•              Pakistan’s known or suspected reprocessing sites (e.g., the New Labs facility at the Pakistan Institute of Nuclear Science and Technology) handle this critical step.
b.            Closing the Loop
•              Because the short cycle discards fuel while most of its fissile potential remains untapped (intentionally so, to keep ²³⁹Pu pure), reprocessing recovers unburned uranium and the newly created plutonium.
•              If operators choose, they can blend the recovered uranium-now possibly enriched with some plutonium-back into fresh fuel elements, continuing the cycle.
c.             Resource Efficiency
•              Continuous or partial reloads, combined with reprocessing, drastically reduce the amount of fresh enriched uranium needed each year to maintain Khushab’s production tempo.
•              While not as resource-efficient as commercial high-burnup reactors, it is optimal for weapons purposes.
B.            Recovering Tritium from Heavy Water and Li-6 Targets
a.            Tritium Extraction Systems
•              When reactors are doped with lithium-6, a significant fraction of   will be created directly in targets or in Li-bearing coolant sections.
•              Specialized tritium extraction facilities (chemical or cryogenic separation steps) are required to separate the ³H from other hydrogen isotopes.
•              Heavy-water cleanup can also yield T, but only if there is an attached tritium recovery plant.
b.            Purification for Weapons Use
•              Weapons-usable tritium needs to be virtually free of other isotopes (especially ²H) and contaminants.
•              Techniques may involve vacuum distillation, isotopic exchange columns, or cryogenic distillation. These are expensive and demand meticulous handling protocols.
c.             Inventory Management
•              Given the short half-life (12.32 years), reprocessing staff must track how much T is lost over time and ensure just-in-time transfers from the reactor/coolant loops to storage before decay lowers its effective concentration.
•              The synergy of frequent reactor refueling and regular extraction cycles helps keep a steady flow of fresh T ready for warhead assemblies.
C. Short Refueling Cycles: Operational Footprint
a.            Batch vs. Continuous Replenishment
•              Batch Refueling: The reactor is shut down at the end of a short (100-200 day) run, all fuel is removed, and fresh or recycled fuel is loaded.
•              On-Power Refueling: Possible in some PHWR designs, where spent bundles are swapped out gradually so that the core remains critical without lengthy outages.
b.            Frequent Fuel Transfers
•              Whether batch or continuous, the net result is significantly more frequent spent fuel transfers to reprocessing sites than in a typical commercial reactor.
•              This heightened traffic in spent fuel casks or reprocessing shipments is a key indicator that short-burnup cycles-and thus weapons-grade objectives-are underway.
D.            Closing the Weapons Cycle
a.            Plutonium Metal Conversion
•              Once separated, plutonium nitrate or oxide solutions undergo further chemical processing to yield plutonium metal-the form typically needed for nuclear warhead cores.
•              Pakistan’s specialized metallurgical and chemical labs oversee these final steps, ensuring the Pu meets the design specifications of the warhead.
b.            Warhead Assembly
•              After plutonium metal and high-purity tritium are secured, warhead components (e.g., implosion systems, neutron initiators) are brought together in specialized weaponization facilities.
•              This final assembly is presumably integrated with delivery vehicles-ranging from short-range ballistic missiles to cruise missiles-forming the operational deterrent force.
c.             Annual Production Outlook
•              Frequent reprocessing + short cycle ->  a steady, if modest, throughput of  60+kg WGPu annually and  130-140g T (under realistic conditions).
•              Enough to sustain 170 existing devices and produce 3-5 new warheads each year, reinforcing Pakistan’s incremental arsenal growth policy.

Together, spent fuel reprocessing and tritium recovery provide the crucial last links in Khushab’s nuclear supply chain. Only by extracting and refining the plutonium to metallic form-and concurrently purifying tritium-can the raw output of these heavy-water reactors be transformed into fully assembled, boosted nuclear warheads. This cycle underscores the role that reprocessing plants and specialized tritium-handling facilities play in underpinning Pakistan’s nuclear weapon capabilities.

Conclusion and Outlook
Over the course of these sections, we have traced how the Khushab nuclear complex in Pakistan accomplishes a dual mission of producing weapons-grade plutonium (WGPu) and tritium (³H) through carefully managed reactor operations, specialized fuel choices, and systematic reprocessing. By leveraging heavy water moderators, uranium metal fuel, and lithium-6 doping, Khushab’s four heavy-water reactors can employ short irradiation cycles to secure high-purity plutonium (with ²³⁹Pu at 90 wt%) while also accumulating enough tritium to sustain and modestly expand its nuclear arsenal.

Kartikeya Sethi is the Founder CEO of Vel Atomics

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The world first became aware of Russia’s Poseidon torpedo in 2018, when it was revealed in a speech by Russian President Vladimir Putin. The torpedo is a nuclear-powered, nuclear-armed, autonomous underwater vehicle designed to deliver a massive payload of explosives.

The Russians claim to have tested the Poseidon torpedo in November 2019. According to them, the Russian Navy conducted a successful test launch of the Poseidon torpedo from a submerged submarine. The test was conducted in the White Sea and was reportedly successful.

However, it should be noted that there is no evidence of the Poseidon being tested, especially over an intercontinental range. There are serious doubts about its operational status. Some sources have made exaggerated claims about Poseidon’s ability to destroy coastal infrastructure.

In addition to the above they will not be able to test the Poseidon for two reasons :

If a nuclear detonation test went wrong and the ensuing radioactive tsunami hit Crimea, it might make the situation extremely difficult for Russia.

Without a nuclear weapon, a test failure would raise questions about the effectiveness of Russia’s nuclear deterrent.

There are other torpedoes with similar capabilities to the Poseidon in the world’s navies. For example, the United States Navy has the Mark 48 torpedo, which is a nuclear-powered, nuclear-armed, autonomous underwater vehicle with a range of up to 6,000 kilometers and a speed of up to 50 knots. Additionally, the Royal Navy has the Spearfish torpedo, which is a conventional-powered, nuclear-armed, autonomous underwater vehicle with a range of up to 10,000 kilometers and a speed of up to 50 knots.

The Poseidon Torpedo or Status-6 is an autonomous, nuclear-powered unmanned underwater vehicle capable of delivering nuclear warheads.

The designer claims it can autonomously navigate to the intended target, travelling at speeds up to 200 km/hr, and deliver a 100 MT nuclear warhead that will generate tsunami waves 500 meters in height, all while remaining undetected throughout its journey to the target.

Several Russian submarines are believed to be armed with the Poseidon torpedo. These include the Borei-class submarines, the Yasen-class submarines, and the Lada-class submarines. Additionally, the Russian Navy is reportedly planning to equip its new Project 885M submarines with the Poseidon torpedo.

The first question that comes up is, “How will the torpedo navigate to the intended target with enough accuracy and without being detected?” Inertial Navigation System (INS) alone is not going to be sufficient. It would have to be augmented with seabed Terrain Controur Matching (TERCOM) and Artificial Intelligence (AI). Given the size of the guidance, navigation and control compartment in the torpedo, it would make sense if they included a backup legacy navigation system such as GLONASS and rode extremely low frequency beacons (82 Hz) using phase adjustment, whose transmitters would be land-based (at Murmansk and the others might be based near Venezuela or Cuba). During a war, the first targets would be these land-based transmitters; the torpedo would then switch to the GLONASS/INS system. The extra space in the guidance, navigation & control (GN&C) compartment could be used for the equipment for seabed TERCOM, data for the predetermined paths, autonomous switching between operation modes, terrain avoidance, drift calculation modules, etc.

The next aspect is the speed of the torpedo. The design bureau claims achievable speeds of around 200 km/h. To achieve these speeds, a high-power output reactor would be required. The downside is that it would make the torpedo very detectable and lose out on its surprise element. We can expect a reasonable output from the power plant. Given the dimensions of the platform, the reactor compartment is around 6–8 ft in length, and a rough estimate of the diameter is around 6-6.5 ft. Now the catch is that if the shielding is high to lower the radiation and its thermal signature on any anti-submarine warfare (ASW) platform, the internal core dimensions would reduce significantly and the output could be expected to be a lot less (around 3-5 MW). The other case is that if the shielding is minimal and the reactor core would be a bit larger with more space to accommodate coolant volume, the expected output would be around 6-7 MW. The choice of reactor would be a gas-cooled reactor, as the power output mentioned above would be more achievable with the same. In the event that a pressurized water reactor is used, the coolant pumps would basically advertise the location of the torpedo to any observer, making it a less desirable choice.

During engagement, assuming the torpedo moves at very slow speed towards the coastal target or a carrier battle group taking many weeks and then sprints at high speeds towards the target near the surface. The onboard batteries would need to be charged, assuming a low duty cycle, the output from the reactor and the storage capacity of the batteries, it would make adjustments in its final approach. The batteries could be Li-Ion batteries. Considering silent operations, the charging process could take many days and finally when the sprinting is required it would dispense the battery power making the high speeds viable. It could be possible to do both super slow and super fast propulsion. For super slow movements, the reactor could operate at 70-80% capacity without engaging the coolant pumps. As speculated Highly Enriched Uranium (HEU) would be the fuel to make this possible. Minimizing movement of control rods would be essential in making the platform even more stealthy. The claim of speeds of up-to 100 knots can be disputed and brought down to a reasonable 67-74 knots range (after assuming the weight of the platform, the power requirements for cooling systems, the GN&C systems). During detonation of the warhead, the reactor would also likely undergo fission and provide additional yield to the blast.

The yield of the warhead is claimed to be around 100 MT which might not conform to the dimensional limitations of the Poseidon’s warhead compartment. The rough estimate of the compartment dimensions for the nuclear warhead are around 9-11 ft in length and 6.5 ft in diameter. The warhead design has certain limitations even if it is of the relatively newer generation ones. The amount of fissile material, the arrangement for the primary and secondary or the third stage would require more space and volume. We can consider the Tsar Bomba as a benchmark in regards to the dimensions. Over the course of years, the material and geometrical considerations have evolved but they still conform to the basic design laws. The amount of tritium required and the pressure required would be considerably larger. The metallurgical considerations for the plutonium pit of such size would severely limit the yield. The geometric setting for the x-ray transport phenomena to maximize the yield would stretch out the warhead. Keeping the above into consideration, the current size of the Poseidon’s warhead would be limited to anything under 10-15 MT (theoretically).

Another important consideration is the intended target, the most probable target as has also been conveyed through the propaganda is the heavily populated coastal regions. According to my calculations, the most probable target would be the region where two tectonic plates share their boundaries. There are coastal regions, especially cities and landmasses in very close proximity to the boundary of the North American Plate and the Pacific Plate. The buildup of stress in the San Andreas Fault might be quickly released if a detonation or a series of detonations of such yield take place. The long predicted earthquake might come a little earlier and cause devastation to the landmasses in the proximity. After the detonation in the near surface region of such landmasses, a Tsunami can be expected but the tide of the Tsunami might not exceed 100-150 ft. It will submerge some areas, but the subsequent destabilization of the San Andreas fault would be a much bigger concern.

Theoretically, the Poseidon torpedo is capable of causing a huge tsunami. Its yield of up to 100 megatons, can cause a devastating tsunami if detonated in the ocean. It was claimed that the United Kingdom could potentially be drowned in a tsunami from a Poseidon torpedo attack. As it is, the UK is also at risk of tsunamis generated by submarine landslides, which can occur when large amounts of sediment are displaced by an earthquake. Additionally, the UK is at risk of tsunamis generated by volcanic eruptions, which can occur when large amounts of magma are displaced by an eruption.

One way to counter the Poseidon is through the use of anti-torpedo systems, such as the US Navy’s Mk-48 Advanced Capability (ADCAP) torpedo. This system is designed to detect and intercept incoming torpedoes, allowing for a greater chance of successful defence against the Poseidon. Additionally, other countermeasures, such as acoustic decoys, can be used to confuse and divert the torpedo away from its intended target.

Verdict : While the Poseidon Nuclear Torpedo excels at fulfilling the internal and external propaganda, but the claims made by the designer need to be fully validated.

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Biden said, “What I think is maybe one of the most dangerous nations in the world, Pakistan. Nuclear weapons without any cohesion.”

The US president made the comments at the reception while talking about the ongoing Russia-Ukraine conflict and how it has impacted the globe. He also spoke about Washington’s ties with other countries.

It is pertinent to note here that Biden’s comment surfaced almost three weeks since the US and Pakistan materialised a defence deal on the F-16 fleet. On September 26, US State Secretary Antony Blinken said it was Washington’s responsibility and obligation to help provide military supplies ‘to whoever’ required them for military sustenance.

“To be very clear, this is a sustainment programme for F-16s that Pakistan has long had. These are old planes and systems that they already have. We have a responsibility and obligation to whoever we provide military supplies to maintain and sustain them. Pakistan’s programme bolsters its capability to fight terror and terrorist threats emanating from Pakistan or from the region,” Blinken had said.

It may be noted that Blinken was posed a question pertaining to the F-16 deal with Pakistan after Indian foreign affairs minister S Jaishankar questioned the ulterior motive of the pact.

Voicing his doubts about the merits of US-Pakistan bilateral ties, Jaishankar had said, “…Very honestly, it’s a relationship that has neither ended up serving Pakistan well nor serving American interests. So, it’s really for the US today to reflect on what the merits are of this relationship (US-Pakistan ties) and what they get by it.”

Shortly after Jaishankar approached the US-Pakistan F-16 deal with a view, Pakistan was quick to justify it. Issuing a statement, Islamabad said, “Responding to media questions about unwarranted remarks by the Indian Minister for External Affairs, the spokesperson said that Pakistan has a longstanding and broad-based relationship with the United States.”

“India is strongly urged to respect basic norms of inter-state relations and refrain from commenting on the bilateral ties between the US and Pakistan. India also needs serious introspection of its diplomatic conduct,” Pakistan’s foreign affairs ministry said.

The comment on Pakistan comes at a time when Islamabad may be ejected from the grey list of the Financial Action Task Force (FATF), a global financial watchdog. Pakistan has been listed under the category owing to deficiencies in counter-terror funding and anti-money laundering policies.

The anti-terror funding laws failed to comply with FATF standards, thus, Pakistan has been named on the ‘grey list’ since June 2018.

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Russian President Vladimir Putin made a thinly veiled threat to use nuclear arms in a speech, 21 September, in which he announced the mobilization of reservists following Ukrainian gains on the ground.

Secretary of State Antony Blinken, in an interview broadcast 25 September, confirmed reports that the United States has sent private warnings to Russia to steer clear of nuclear war.

“We have been very clear with the Russians publicly, and, as well as privately, to stop the loose talk about nuclear weapons,” Mr. Blinken told the CBS News program “60 Minutes” in New York on the sidelines of the U.N. General Assembly.

“It’s very important that Moscow hear from us and know from us that the consequences would be horrific. And we’ve made that very clear,” Mr. Blinken said.

“Any use of nuclear weapons would have catastrophic effects for, of course, the country using them, but for many others as well.”

Jake Sullivan, President Joe Biden’s national security advisor, said in a separate interview 25 September that the United States has warned Russia at “very high levels” of “catastrophic consequences” for using nuclear arms.

 ‘Scare the whole world’

The United States and its allies would “respond decisively,” Mr. Sullivan said on CBS’s “Face the Nation.”

“We have been clear and specific about what that will entail.”

Russia and the United States are the world’s largest nuclear weapons powers, but separate from the threats of planetary destruction, Russian military doctrine permits the use of tactical nuclear weapons on the battlefield to force an enemy to retreat.

Russian Foreign Minister Sergei Lavrov, asked during a news conference 24 September at the United Nations about Mr. Putin’s comments, said only that Moscow’s doctrine “is an open document.”

President Volodymyr Zelensky told “Face the Nation” that Mr. Putin’s veiled nuclear threat “could be a reality,” saying Russian military activity at nuclear power plants in Ukraine are “the first steps of his nuclear blackmail.”

“He wants to scare the whole world,” the Ukrainian leader said of Mr. Putin.

“I don’t think he’s bluffing. I think the world is deterring it and containing this threat. We need to keep putting pressure on him and not allow him to continue,” Mr. Zelensky added.

No country has used nuclear weapons on the battlefield except the United States in 1945, when it destroyed the Japanese cities of Hiroshima and Nagasaki, killing more than 200,000 people. Imperial Japan surrendered days later, ending World War II.

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In a televised address to the Russian people on 21 September, Putin explicitly raised the specter of a nuclear conflict. Despite being regarded as a very low likelihood scenario, the potential implications of such a scenario are huge.

This article tries to give the reader-at-large an idea about what is involved in launching a tactical nuclear strike.

The push for partial mobilization is bound to escalate the situation in Ukraine. Losses are mounting exponentially and with the influx of inexperienced conscripts who lack any meaningful knowledge of the weapon systems would further make the situation even more dire.

There is no justification to use nuclear weapons in a conflict with a non-nuclear state. But according to Russia, the only feasible way to put an end to the conflict is to use nuclear weapons. The chances of a nuclear device detonation have become uncomfortably high.

Russia’s Strategic Rocket Forces possess a wide variety of nuclear weapons platforms and devices. Russia currently has approximately 6000 warheads. They vary in their yield and the safety mechanisms. Most of the devices are equipped with a standard dialable yield system, which according to the target can be adjusted. They also possess a wide variety of platforms to deliver the said devices ranging from ICBMs to artillery shells.

As per the Russian state, current conflict would call for the use of tactical nuclear weapons to deter Ukrainian advances all the up to the border of Russia. The most important factor is the launch time preparedness. The long range ballistic missiles are at the highest level of readiness. The inherent problem of long range liquid fueled missiles meant that they had to be fueled immediately before launch, this was solved by the R-36 series which were fueled only once, when they are placed in the silos. After that the missiles are ampulised/sealed and kept in this state ready for launch. As a result, the time needed to wind up the guidance system’s gyroscopes became the main constraint on launch readiness rather than the several hours that the missile previously needed to launch.

R-36M missiles were the first liquid-fuel missiles that used a so-called cold launch method, in which the missile main engine did not start until the missile had been ejected from the silo by a special charge: a pressure accumulator. This launch method reduced the heat and acoustic load on the missile and allowed the fuller use of silo volume.

The development of the automated system of combat management and the introduction of third-generation missile systems with on-board computers provided the RVSN the technological capacity to remotely alter missile flight assignments and alter nuclear force use scenarios in response to changing circumstances. Since the flight trajectory of missiles moving along the combat route must constantly be recalculated as the location of the launchers changes, the adoption of fourth-generation systems (the R-36M2, RT-23UTTH, and Topol) provided the capability for quick retargeting, which was crucial in the case of mobile systems. Therefore, there were no new technological challenges while changing the targeted coordinates.

During the pre-war time silo-based missiles would have been reprogrammed with “neutral” flight assignments (aimed at targets in the ocean). Fourth-generation systems are now on combat duty with zero flight assignments. These changes were largely symbolic, however, because it takes no more than a few minutes to retarget systems in accordance with operational plans for their use.

It is the tactical systems that require more time for getting ready to be deployed on the battlefield. Russia has many of them. The warhead must be prepared, mated to the desired platform (usually cruise missiles but in some cases smaller warheads can be mated to the S-300/400 series to deny the airspace to the enemy).

From transporting the warhead to the location, calibrating the gyroscopes (if the device has them), programming the detonation yield, testing the on board power system and finally mating the device to the platform on the appropriate bus. This will take several hours and will be detected by satellites, drones and people.

For instance, if Russia wishes to deploy the Nuclear weapon from a ground based launcher to detonate above the Black Sea/forward areas of Donetsk. It is highly likely the platform of choice is going to be a Mig-31. It is important to know that the control of the missile launch will be remote and may not be in the hands of the pilot.

If they choose to use a ground based launcher(static or mobile), it is highly likely the following steps will be followed :

1. The General Staff gives the proper directives to the armed forces’ services regarding the use of nuclear weapons when the decision to use nuclear weapons has been taken and the precise scenario for their use has been determined.

2. The Central Command Center of the General Staff (which serves as the Supreme High Command Central Command Center) transmits the necessary authorization codes and unlocks certain launchers to issue the command to employ nuclear weapons.

3. The combat management signal for the Rocket Forces initially travels to the Strategic Rocket Forces Central Command Center before being forwarded to the regiments whose launchers are to be employed.

4. The on-duty staff must input the authorizing codes and launch the missiles when the order to employ weapons and the authorizing codes have been sent. The command and control system also allows for the capability of firing missiles without the involvement of personnel on lower levels directly from the Supreme High Command Central Command Center.

5. Automated launch preparations begin as soon as the launcher receives the launch command. The response time—the period of time between the transmission of the launch command and the actual launch—depends on the missile and launcher, as well as their condition at the moment the command is received.

6. Prior to launch, the missile’s guidance system must be activated (the switch to onboard power supply, the activation of the gyros, etc.), and the first-stage propulsion system (or the pressure accumulator in a cold-launch system) must be ignited.

7. When the launch command is received, the transporter-launcher (ground or rail) stops, the launcher is secured in the soil with hydraulic supports, and the canister containing the missile is raised to a vertical position. After this, the pressure accumulator is ignited and the missile is fired from the canister.

Part 2 will cover the launch to detonation and aftermath

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Before the attack on Ukraine, the five nuclear-haves under the Non-Proliferation Treaty (NPT) — the United States, the United Kingdom, Russia, China, and France — had reached agreement that the use of nuclear weapons could be justified only as a purely defensive measure in response to a nuclear or large-scale conventional attack. In January 2022, those five countries issued a joint statement affirming that “a nuclear war must never be fought and can never be won.” A month later, Russia invaded a non-nuclear country, Ukraine, and threatened nuclear attacks against anyone who tried to help that country.

President Vladimir Putin and other Russian officials have been ominously threatening to use nuclear weapons in the war against Ukraine. The long-range ballistic missiles deployed on land and on submarines are Russia’s only nuclear weapons available for immediate use.

In 2021, during a training exercise involving about 200,000 troops, the Russian army practiced launching a nuclear assault on NATO forces in Poland. An intentional or inadvertent Russian attack on a NATO country could be the beginning of World War III.

If Russia decides to attack Ukraine with “tactical” nuclear weapons, the transportation to military bases, mating with cruise or ballistic missiles, loading on planes, etc will observed by the US in real time.

President Joe Biden has made clear that any use of nuclear weapons in Ukraine would be “completely unacceptable” and “entail severe consequences.”

Likely Scenarios

Russia might use a nuclear weapon by
• Detonation over the Black Sea, causing no casualties but demonstrating a resolve.
• A decapitation strike against the Ukrainian leadership.
• A nuclear assault on a Ukrainian military target.
• The destruction of a Ukrainian city, causing mass civilian casualties.

US Response

According to The New York Times, the Biden administration has formed a Tiger Team of national-security officials to run war games on what to do if Russia uses a nuclear weapon.

Biden administration’s strategy is of “deliberate ambiguity.” But everyone hopes that some form of back-channel diplomacy is secretly being conducted. The Russians have probably been given a message about how harshly the US might retaliate if they cross the nuclear threshold. But misunderstandings, miscommunications, and mistakes can lead to a nuclear catastrophe.

Some experts feel that if Russia uses a nuclear weapon in Ukraine, American nuclear retaliation should be the last resort. Instead, the US should opt for horizontal escalation, solely with conventional weapons. Russia’s Black Sea fleet might be sunk in retaliation, and a no-fly zone could be imposed over Ukraine, even if it meant destroying anti-aircraft units on Russian soil.

During the summer of 2016, the US national-security team secretly staged a wargame in which Russia invades a NATO country in the Baltics and then uses a low-yield tactical nuclear weapon against NATO forces to end the conflict on favorable terms. The security team reached widely divergent conclusions about what the United States should do. Some decided that the United States had no choice but to retaliate with nuclear weapons. Choosing a suitable nuclear target proved difficult, however. One committee recommended a nuclear attack on Belarus—a nation that had played no role whatsoever in the invasion of the NATO ally but because it was a Russian ally.

Others argued that retaliating with a nuclear weapon would be a huge mistake. It would be more effective to respond with a conventional attack, they recommended, and turn world opinion against Russia for violating the nuclear taboo.

Any nuclear attack on Ukraine would inspire global condemnation, especially from countries in Africa and South America, continents that are nuclear-weapon-free zones. China has long supported “negative nuclear assurances” and promised in 2016 “unconditionally not [to] use or threaten to use nuclear weapons against non-nuclear-weapon states or in nuclear-weapon-free zones.”

Others preferred “a muscular diplomatic response” to the nuclear strike, not a nuclear or conventional military response, combined with some form of hybrid warfare. The United States could launch a crippling cyberattack on the Russian command-and-control systems tied to the nuclear assault and leave open the possibility of subsequent military attacks.

Tactical Weapons

During the Cold War, the United States based thousands of low-yield tactical nuclear weapons in NATO countries and planned to use them on the battlefield in the event of a Soviet invasion. In September 1991, President George H. W. Bush unilaterally ordered all of America’s ground-based tactical weapons to be removed from service and destroyed. The United States was developing precision conventional weapons that could destroy any important target without breaking the nuclear taboo. But Russia never got rid of its tactical nuclear weapons.

The weakness of Russia’s conventional forces compared with those of the United States, Perry suggests, and Russia’s relative advantage in tactical weapons are factors that might lead Putin to launch a nuclear attack in Ukraine. Russia may be able to destroy a military target without much radioactive fallout, without civilian casualties, and without prompting a strong response from the United States. There would be an international uproar, but it would not last long.

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Russia’s invasion has killed thousands of people, displaced nearly 10 million, and raised fears of a wider confrontation between Russia and the United States – by far the world’s biggest nuclear powers.

Within days of Russia’s Feb. 24 invasion, Putin put the country’s deterrence forces – which include nuclear arms – on high alert, citing what he called aggressive statements by NATO leaders and Western economic sanctions against Moscow.

Russia’s deputy foreign minister said, on 10 May, that a decision on the possible use of nuclear weapons was clearly set out in Russia’s military doctrine, when asked if Russia would rule out a preemptive tactical nuclear strike on Ukraine. “We have a military doctrine – everything is written there,” Alexander Grushko was quoted by state news agency RIA as saying.

Russia’s official military deployment principles allow for the use of nuclear weapons if they – or other types of weapons of mass destruction – are used against it, or if the Russian state faces an existential threat from conventional weapons.

The decision to use Russia’s vast nuclear arsenal, the biggest in the world, rests with the Russian president, currently Vladimir Putin.

U.S. Central Intelligence Agency Director William Burns said, on 7 May, that Putin believes he cannot afford to lose in Ukraine and cautioned that the West could not ignore the risk of the use of tactical nuclear weapons by Moscow.

“We don’t see, as an intelligence community, practical evidence at this point of Russian planning for a deployment or even use of tactical nuclear weapons,” Burns said. He cautioned, though, that “the stakes are very high for Putin’s Russia.”

Circumstances for Strike

Russia has accused However NATO countries of a “hybrid” confrontation that now “dangerously balances on the edge of open military clash.””Such a move would be able to trigger one of the two emergency scenarios described in our doctrine,” as per Russian strategists, adding “if Western countries try to test our resolve, Russia will not back down.”

Nuclear brinkmanship from Putin has been unprecedented. He ordered a snap nuclear wargame before the invasion and days later put his nuclear forces on high alert. And the Kremlin has repeatedly signaled it could resort to nuclear weapons if it determines the West’s intervention in the conflict goes too far.

As the conflict drags on, and Russia’s conventional forces suffer surprisingly heavy losses while its economy reels, the prospect that Putin might resort to using weapons of mass destruction is increasing. Moscow has already demonstrated that it is willing to use hypersonic missiles for the first time in a war.

A decree signed by Putin on June 2, 2020, said Russia views its nuclear weapons as “exclusively a means of deterrence”. It repeats the phraseology of the military doctrine but adds details about four circumstances under which a nuclear strike would be ordered. These include reliable information of a ballistic missile attack on Russia and an enemy’s attack “on critical state or military installations of the Russian Federation, the incapacitation of which would lead to the disruption of a response by nuclear forces.”

US Intelligence Assessment

Putin could view the prospect of defeat in Ukraine as an existential threat to his regime, potentially triggering his resort to using a nuclear weapon, a top US intelligence official has warned. The warning came in an assessment from intelligence chiefs briefing the Senate on worldwide threats.

The Director of National Intelligence, Avril Haines, told the Senate’s Armed Services Committee that Putin would continue to brandish Russia’s nuclear arsenal in an attempt to deter the US and its allies from extending further support for Ukraine.

The Russian leader would not use a nuclear weapon until he sees an existential threat to Russia or his regime, Haines argued.

But she added that he could view the prospect of defeat in Ukraine as constituting such a threat, the report said.

“We do think that [Putin’s perception of an existential threat] could be the case in the event that he perceives that he is losing the war in Ukraine, and that Nato in effect is either intervening or about to intervene in that context, which would obviously contribute to a perception that he is about to lose the war in Ukraine,” Haines told the committee hearing.

She added that the world would probably have some warning that nuclear use is imminent.

The prediction for Ukraine is a long, gruelling war of attrition, which could lead to increasingly volatile acts of escalation from Putin, including full mobilisation, the imposition of martial law, and if the Russian leader feels the war is going against him, endangering his position in Moscow even the use of a nuclear warhead, the report said.

Putin, who has repeatedly expressed resentment over the way the West treated Russia after the 1991 fall of the Soviet Union, says Ukraine has been used by the United States to threaten Russia.

He justified his Feb. 24 order for a special military operation by saying Ukraine had persecuted Russian speakers and the United States was keen to enlarge the NATO military alliance in a way that would endanger Russia.

The Likelihood

IMR’s assessment of the likelihood of Russia using nuclear weapons, most likely scenario and US response is given below.

Putin is more likely than not to use nuclear weapons in the war in Ukraine if he faces devastating defeat. Nuclear weapons are the ultimate tools of last resort; any rational leader would consider using them if his or her regime (or life) were on the line.

Putin presumably expects his threats will induce NATO to abandon Ukraine. However, if he believes he is facing defeat or a costly stalemate—or has a chance of success through sharp escalation—there is some risk he will carry out his threats.

If Russian forces suffered a humiliating defeat in the campaign to control Donbas, Putin could be pressed by hardliners to deliver on his nuclear threats; but he is unlikely to do so, since this would only galvanize a harsh US and allied response without providing any significant military advantage.

Most Likely Use Scenario

Washington and Moscow have walked away from several treaties to control the deadliest weapons, including one that outlawed intermediate-range nuclear missiles that could threaten Europe.The only remaining nuclear pact between the two sides is the New Strategic Arms Reduction Treaty, which limits deployed strategic weapons to 1,550 each. Biden and Putin agreed last year to extend it until 2026. The treaty does not cover any of the thousands of smaller, or “battlefield,” nuclear weapons in their respective arsenals, including at least 2,000 in Russian stockpiles, according to public estimates.

Putin would seek to create fear instead of rage. Thus, nuclear weapons would be used in Ukraine rather than on NATO territory, and they would be used against military, not civilian, targets. Any attack would likely involve detonating half a dozen low-yield air bursts (in order to minimize fallout) against well-entrenched Ukrainian military positions.

Putin might begin with the ostentatious movement of nuclear forces, such as sending weapons to Russia’s Baltic enclave of Kaliningrad. He could order a “demonstration” or possibly a detonation at a Russian test range.

Putin may hope that just by crossing the nuclear threshold, he would so shock Ukraine and its Western backers—and so terrify allied publics—that they would back down rather than risk further escalation.

The risk of nuclear use through a mistake or blunder is higher than through intent. Many Russian battlefield systems are dual-capable and also designed to unleash both conventional and nuclear or chemical warheads. It could be exceedingly difficult to know when the Russian military has decided to pursue a nuclear option. It is difficult to know if the S-300 battery packs a conventional warhead or a nuclear one.

Likely US and Allied Response

One possible response to Putin’s nuclear use would be to negotiate some kind of resolution in which all parties could declare Potemkin victories and find a solution before nuclear weapons are used.

If the Russian attack caused little damage, NATO might first try to issue an ultimatum with the aim of reaching a settlement on the Alliance’s and Ukraine’s terms.

A non-nuclear military response (eg, conventional strikes on military bases and infrastructure in Russian territory) would probably not be decisive and would appear inadequate to many.

Defending Ukraine may simply not worth risking a nuclear escalation. But there are also serious implications of not doing it. Absence of a US nuclear response would gravely weaken the credibility among both friends and adversaries of the entire strategy of deterring nuclear attack through the prospect of US nuclear retaliation.

If Putin resorted to the use of nuclear weapons, the United States and its allies would need to respond quickly and decisively to ensure that Putin paid a heavy price for crossing the nuclear threshold.

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As part of user trial, Agni-5 was successfully launched, on 27 October 2021, from Abdul Kalam Island, Odisha. According to Ministry of Defence (MoD), the test was in line with India’s credible minimum deterrence policy with the commitment to ‘No First Use.’

Seven Pre-trial Launches

On 19 April 2012, Agni V was successfully test-fired for the first time. On 10 December 2018, a seventh test launch of Agni-V was successfully conducted. It was for the first time that the missile was test-fired in a lofted trajectory. The missile blasted off from a hermetically sealed canister and covered nearly 2,041 km. This lofted trajectory flight was used to determine whether it followed the perfect flight path with close to zero error. This trial completed the Agni-V pre-induction trials.

Development

Agni V is primarily for enhancing India’s nuclear deterrence against China. Until recently, the longest range missile India had was Agni-III, with a range of 3000–3500 km. This range was not sufficient to reach targets on the extreme eastern and north-eastern region of China. Most of the important economic centres of China lay on its eastern seaboard. Even with a range of only 5,000 km, the Agni-V could hit any target in China, including Beijing.

Indian authorities believed that the solid-fuelled Agni-V is more than adequate to meet current threat perceptions and security concerns.

The missile will allow India to strike targets across Asia and into Europe. The missile’s range will allow the Indian military to target all of China from Agni-V bases, in central and southern India, further away from China.

The missile was designed to be easy to transport by road, through the utilisation of a canister-launch missile system, which is distinct from those of the earlier Agni missiles. Agni-V would also carry MIRV (multiple independently targetable re-entry vehicles) payloads being concurrently developed. A single MIRV equipped missile can deliver multiple warheads at different targets.

Agni-V incorporates advanced technologies involving ring laser gyroscope and accelerometer for navigation and guidance. With a canister-launch system to impart higher road mobility, the missile, will give the armed forces much greater operational flexibility than the earlier-generation of Agni missiles. The accuracy levels of Agni-V and the Agni-IV, with their better guidance and navigation systems, are far higher than previous Agni series.

About Agni-5

Propulsion. The Agni-V is a three-stage solid fuelled missile with composite motor casing in the second and third stage. In many aspects, the Agni-5 carries forward the Agni-3 pedigree. With composites used extensively to reduce weight, and a third stage added on (the Agni-3 was a two-stage missile), the Agni-5 can fly significantly more to inter-continental range.

Range. Former DRDO chief VK Saraswat once disclosed the range of Agni-V as 5,500–5,800 km. The Chinese believe that the missile has a range of around 8,000 kilometres. The exact range of the Agni-V missile is classified.

Guidance and control. A ring laser gyroscope based inertial navigation system (RLG-INS) is primarily responsible for guiding the Agni-V to its target. However, Agni-V is equipped with another guidance system called micro inertial navigation system (MINGS) as a backup. These are capable of interacting with Indian and non-Indian satellite navigation systems. Both of these systems have been developed by the Research Centre Imarat. Agni V uses a system on chip (SOC) based on-board computer (OBC) whose weight is around 200 grams for control and guidance. All stages of the missile have nozzle-based control systems.

Mobility. The Agni-5 is specially tailored for road-mobility. With the canister having been successfully developed, all India’s future land-based strategic missiles will be canisterised as well. Made of maraging steel, a canister must provide a hermetically sealed atmosphere that preserves the missile for years. During firing, the canister must absorb enormous stresses when a thrust of 300 to 400 tonnes is generated to eject the 50 tonnes missile. If the missile is ejected using a gas generator from the canister, then the missile could be launched from any pre-surveyed launch location without the need for any pre-built launch site.

The launcher, which is known as the Transport-cum-Tilting vehicle-5, is a 140-ton, 30-metre, 7-axle trailer pulled by a 3-axle Volvo truck.

Anti-satellite version. Dr VK Saraswat said that an ASAT version is technically possible: ASAT weapon would require reaching about 800 km altitude. Agni V offers the boosting capability and the ‘kill vehicle’, with advanced seekers, will be able to home into the target satellite.

MIRVs. Agni-V is expected to feature Multiple independently targetable reentry vehicle (MIRVs) with each missile being capable of carrying 2–10 separate nuclear warheads. Each warhead can be assigned to a different target, separated by hundreds of kilometres; alternatively, two or more warheads can be assigned to one target. MIRVs ensure a credible second strike capability even with few missiles. According to DRDO sources, a MIRV payload would be significantly heavier, since it would consist of several nuclear warheads, each of them weighting about 400 kilogrammes. A 5-warhead MIRV, therefore, would weigh two tonnes.

The MIRV capability of Agni-V has been tested indirectly in a discreet manner, according to Bharat Karnad, who was involved in drafting India’s nuclear doctrine. Karnad states that the MIRV capability of the missile’s guidance system on chip (SOC) was tested during the multi-satellite PSLV launch on 25 February 2013.

Global Reactions

When India tested the Agni-V missile for the first time in 2012, then China’s foreign ministry spokesperson, Liu Weimin stated, “China and India are both emerging powers. We are not rivals, but cooperative partners.”  He further stated, “China always maintains that preserving the strategic balance and stability in South Asia is conducive to peace and prosperity of regional countries and beyond.”  But state run daily, Global Times reported, “India was being swept up by missile delusion” and that China’s neighbours could never win an arms race with China.” In 2017, China’s state run Global Times accused India of violating UN restrictions on range of missiles over the Agni-IV test and instead claimed that Pakistan should also be allowed the same privileges.

The United States views India as a strong partner in the Indo-Pacific Region to counter China’s growing influence also refrained from criticising India’s 2012 Agni-V test and instead applauded India’s non-proliferation efforts then. This came as a stark difference between how the US viewed India’s missile capabilities from the early 2000s and now.

Pakistan on the other hand reacted to Pakistan centric Agni tests with tit-for-tat tests. For instance, when in 1999, India tested its Agni-II missile, Pakistan followed suit by testing the Ghauri missile followed by the Shaheen-I missile. In 2003, Pakistan’s Information Minister, Shaikh Rashid warned India that such tests conducted by India would not help New Delhi to “establish its supremacy in the region.” Prior to this, in 2001, Pakistan reacted to Agni-II missile criticising India, “India’s nuclear ambitions, which are clear from its draft nuclear doctrine announced in 1999, have a destabilising effect on the region.” In fact, just after India’s testing of China-centric Agni missiles, Pakistan in March 2018, acquired a powerful missile tracking system from China that is expected to speed up Pakistan’s ability to develop MIRV technology. 

Nuclear Deterrence

It is crucial for India to develop the Agni missile system as a deterrence against China through second-strike capability. China though has adopted a policy of “no-first-use”, such a policy does not apply to territories that China considers to be a part of its own territory. This has been with Taiwan and India’s Arunachal Pradesh as China considers them to be a part of its own territory.

Agni constitutes the backbone of India’s land-based nuclear deterrence just like the Shaheen category ballistic missiles for Pakistan and the Dong Feng category missiles for China.

The Agni category missiles are solid propelled ballistic missiles, ranging from short range missiles to intermediate range missiles (700-5000kms) with road and rail mobility providing greater chances of survivability during an enemy attack. This strengthens its scope of launching a counter/second strike. This makes India one of the few countries in the world with the ability to potentially decapitate its enemy by preserving its arsenal in the first attack from the enemy.

Solid propulsion systems, use of increased stages to increase ranges, advanced guidance and navigation system equipped with the missile, easy mobility – all these characteristics in a missile make the system more credible and reliable thereby strengthening India’s strategy of “credible minimum deterrence.” Mobility makes the missiles more easily survivable to enemy attack thereby strengthening their ability to launch “counter/second strike” vis-à-vis adversaries. 

With two neighbours with nuclear capability, India needed to have nuclear weapons delivery systems that could not only carry nuclear warheads but also be able to successfully deliver the same despite enemy defence by denial mechanisms. For instance, canister launched missiles are more agile and capable of dodging enemy radars and also spy satellites.

Though it is not clear if Agnis would be based in silos also, there is a possibility that a small number of missiles are silo-based with dummy silos too to evade missile attacks. It is also possible that over the years, India has also hardened the silos to avoid the enemy from attacking and destroying the missiles kept in the silos. 

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