Nuclear weapons at sea – is their use viable?

Against the background of the War in Ukraine, the spectre of nuclear conflict has re-emerged from the wilderness of a Cold War past where it has spent the last three decades. While the use of nuclear weapons has remained a prospect all should wish to avoid, it has nonetheless remained a stubborn strategic possibility. As such, it is worth examining the topic from the standpoint of nuclear weapon employment in a modern-day naval conflict.

Throughout much of the 20th century, a presumption that warfare at sea could involve the employment of nuclear weapons underpinned force design. The staying power of vessels against missile attacks, for example, was deprioritised partially because of an assumption that on a nuclear maritime battlefield, should vessels fail to intercept incoming targets, they would largely become non-survivable.^[1] Nuclear-armed mines and depth charges were also an important part of the arsenals of both sides during the Cold War as a means of achieving area effects against elusive targets such as submarines.^[2]

For much of the Cold War, official US policy was that nuclear use against American assets at sea would be treated as being no different from a nuclear attack anywhere else. However, at the time some scholars questioned whether this was indeed a credible deterrent – after all, unlike tactical nuclear use at scale on land, the use of nuclear weapons at sea would inflict only military casualties.^[3] Against a continental power such as the USSR the challenge was that most forms of nuclear retaliation which would be damaging enough to be credible would necessarily have to target the Soviet homeland and would represent strategic nuclear use rather than the tactical employment of nuclear weapons.

The theory that battlefield nuclear employment at sea could be deterred by the threat of strategic escalation was never tested but there are reasons to believe that this threat was not regarded as credible. This has ramifications for both the conduct of nuclear deterrence under contemporary conditions and the employment of naval forces in the emerging operating environment.

Thinking about nuclear conflict at sea, at least in public discourse, has largely receded with the assumption often being that in the event of a nuclear escalation the character of a conflict has altered to the point where previously held assumptions about warfighting no longer hold. In effect, all nuclear use is to be treated as strategic, with the ramifications that this entails being part of what is expected to deter an opponent. While there is something to be said for strategic ambiguity as a deterrent strategy (insofar as this leaves an opponent without clear consequences to plan against and mitigate) there is some evidence that, at least in the European theatre, this may not be sufficient.

Russian Naval Planning

It is of note that Russia’s planning document ‘Fundamentals of the state policy of the Russian Federation in the field of naval activities for the period until 2030’ explicitly identifies “the capability of the Navy to damage an enemy’s fleet at a level not lower than critical with the use of non-strategic nuclear weapons” as a core naval function.^[4]

It is in many respects unsurprising that this should be the case. On the one hand, Russia has demonstrated that its capacity for conventional targeting at sea is limited at best, particularly in what the Russians identify as the areas beyond their coastal defensive zones (out to slightly over several hundred kilometres from Russia’s coasts). Russia has largely failed to replace the Soviet era Tselina and Legenda electronic intelligence (ELINT) and radar-equipped satellite constellations. The Pion and Lotos satellites which collectively form Russia’s Liana constellation have only been launched in limited numbers, meaning that Russia can expect only intermittent situational awareness at long distances beyond its coastlines.^[5] Other methods of surveillance such as the use of commercial satellite imagery or data from over the horizon (OTH) radar such as the Polsodnyukh and Kontainer are limited either by latency or a lack of granularity. The margin of error on the average OTH radar against maritime targets, for example, is up to 40 km.^[6]

Many of these limitations have been visible during the ongoing conflict in Ukraine. Over the course of this conflict, Russia failed to sink Ukraine’s last remaining surface combatant, the Yuri Olefirenko, as the latter was conducting coastal bombardments off the Kinburn Spit and Kherson, eventually sinking the vessel in port. A failure to sink a dynamic target in a highly congested battlespace does not bode well for Russian efforts to target vessels such as aircraft carriers at what will likely be engaged at considerably greater distances. Furthermore, the Russian capabilities most relevant to maritime strike such as the Tu-22M3 Backfire bomber are available in relatively limited numbers compared to the Cold War. Russia fields 63 Backfires at the time of writing and would likely have fewer remaining in service during a major conflict.

As such, the likely heavy losses taken by the Backfire force in any attack on an allied maritime component would mean that, if unsuccessful, Russia would have squandered an important strategic capability, which also forms a component of its nuclear triad, for limited effect. Other capabilities such as nuclear-powered attack submarines (SSNs) are also available in far more limited numbers than was the case in the Soviet era – meaning the Russians have a more slender margin for error as the loss of these capabilities cannot be countenanced unless targets of commensurate value are destroyed.^[7] It is thus vital for the Russians that if strategic capabilities are committed to the attack under conditions where western forces enjoy greater situational awareness, the odds of success are maximised.

Nuclear weapons could play an important role for the Russians as an offset. However, as will be discussed in subsequent sections, their utility at sea should be contextualized. Nonstrategic nuclear weapons and even strategic capabilities cannot easily be used as an area effect tool to destroy stronger fleets. They can, however, influence important aspects of maritime competition.

Nuclear weapons and anti-surface warfare – its importance and the need for caveats

It should thus not be entirely surprising in the context of the above discussion that Russia retains an emphasis on nuclear use at sea within its naval doctrine. It is, at least in theory, conceivable that the use of nuclear weapons at sea could mitigate the impact of an imperfect kill chain. This being said, there are certain limitations to nuclear use at sea which should also be borne in mind.

There are, broadly speaking, three ways in which a nuclear weapon might be used against a vessel. The first is the destruction of either a vessel’s hull or its superstructure through the overpressure generated by an airburst of a nuclear armed missile. Secondly, the thermal energy generated by a nuclear detonation can harm crew members – though this will primarily affect individuals above decks, and since the Cold War vessels have been designed to minimise crew exposure in this area. Third, the shockwave from an underwater detonation can, in principle, physically destroy a hull.

To mission kill a vessel such as an Arleigh Burke class destroyer, a nuclear detonation would need to achieve an overpressure of around 48 kPa (7 psi).^[8] While comparable data does not exist regarding aircraft carriers, it is worth noting that when landing vertically an aircraft such as the F-35B generates around 18,144 kg (40,000 lb) of pressure which would imply that carrier flight decks can sustain considerably more pressure. However, there is no reason to believe other superstructure elements such as the castle should be less resistant to pressure than those on an Arleigh Burke.^[9]

Based on data gathered from Operation Crossroads, which saw the US Navy Test a 23 kt nuclear weapon against a combination of captured Japanese vessels and obsolete US assets, we can assess that a comparable nuclear weapon could achieve this level of overpressure against a DDG at a distance of around 1.2 km.^[10] This would be comparable to the nuclear payload carried on a missile such as the Russian RPK-6/RPK-7 (SS-N-16 Stallion).^[11] On the one hand, this introduces certain advantages – a missile can miss by a margin and still achieve effects. However if, for example, a ballistic missile is within 1.2 km of its target, a manoeuvring re-entry vehicle should be able to guide it to its intended target with a conventional payload.^[12] This would also hold for an active seeker equipped cruise missile flying at a high altitude. In other words, if an opponent’s reconnaissance and targeting system is refined enough to locate a high-value target with sufficient fidelity to place a missile within roughly a kilometre of its destination, it can complete a kill chain with conventional munitions.

A cruise missile such as the Russian KH-101/102 will carry a considerably larger payload of 250 kt meaning that it would generate comparable levels of overpressure at longer distances of around 2.88 km.^[13] However, to get within roughly 3 km of an aircraft carrier, a high-flying missile (which would be necessary in order to cause an airburst) would have had to have evaded all of the defences of a vessel barring its CIWS – added to which, the use of a 250 kt warhead is a rather uneconomical and high-risk means of defeating terminal phase defences.^[14] If the means to defeat the other layers of a ship’s IAMD can be arrived at, avoiding terminal phase defeat should be possible without the need for nuclear escalation.

An alternative might be bracketing an area with a salvo of nuclear-tipped cruise or ballistic missiles. However, in order to achieve area effects over the roughly 20 km² area within which a ship might be if tracked on the basis of a source such as shore-based OTH radar, a large number of nuclear-tipped warheads would need to be used. This number would grow larger still given that planners would necessarily need to account for the fact that a large part of an incoming salvo would likely be intercepted by shipboard air defences – something evidenced by the air and missile war around Kyiv, for example.^[15] Preparing such a salvo would thus require potentially hundreds of low yield warheads to be moved from storage sites to airbases in which strategic aircraft were positioned – raising the prospect that an opponent could not distinguish preparatory activity from preparations for a wider nuclear attack. Moreover, even if an opponent did distinguish the intended targets of an attack and recognised that maritime platforms are the intended vector, this visible preparatory activity would incentivise the suppression of launch platforms with conventional deep strike capabilities.

Undersea detonations – a more viable approach

The detonation of a nuclear warhead underwater might represent a more fruitful method of nuclear use at sea. The shock waves generated can potentially be used as a means of anti-surface warfare (ASuW), a crude means of both countering submarines and disrupting undersea sensor networks such as the US’ Integrated Undersea Surveillance System (IUSS). Indeed, this was a use case for both nuclear mines and nuclear-armed torpedoes during the Cold War. The shock wave produced by the detonation of a 100 kt weapon underwater can generate 18,616 kPa (2,700 psi) of pressure at a distance of around 1 km.^[16] During the Cold War, tests such as the U.S Navy’s 1955 Wigwam underwater nuclear test demonstrated that a 30 kt nuclear weapon could sink a contemporary submarine at a range of 1.6 km (1 mile) – although modern submarines would enjoy greater pressure resistance than their early Cold War counterparts.^[17] An even larger payload such as the estimated 2 Mt payload on the Russian Poseidon would, of course, produce comparable levels of overpressure at even greater distances.^[18]

However, once more, ASuW is the least-fruitful use case. A large, fast-moving nuclear torpedo should in principle be detected and engaged by anti-submarine warfare (ASW) capabilities at well beyond the distances at which they would be effective at generating an effective shock wave. It should be noted, after all, that ASW capabilities are expected to hold at bay cruise missile equipped submarines using a combination of undersea sensors, maritime patrol aircraft (MPA) and the organic ASW capabilities of a surface force.^[19]

There is another challenge to using nuclear armed torpedoes as an ASuW capability. When shock waves are generated by an underwater detonation, particularly when close to the surface of the ocean, the upward-travelling waves will rapidly encounter the surface, and thus air, which is a much less rigid medium than water. This contact with a less rigid medium leads to rarefaction – that is, a negative pressure wave being reflected back into the water. The interaction between the initial positive pressure shock wave and the reflected negative pressure wave causes a net reduction in water shock pressure.^[20] Consequentially, when objects are near the surface of the water, the effects of a shock wave dissipate more rapidly. Thus, for example, during the Swordfish nuclear tests 10 kt RUR-5A anti-submarine rockets (ASROCs) were launched to distances of about 2.5 km from the destroyer USS Agerholm without the launch vessel facing risks from overpressure.^[21] Notably, 2.5 km is well within the range of most modern conventional torpedoes such as the MK 48 ADCAP. As such, it is unclear why, if a submarine has slipped to within 2.5 km of its surface target, it would not use a conventional torpedo. It is for this reason that nuclear weapons were, during the Cold War, largely viewed as a reversionary capability to be used in the event that unexpected flaws in conventional capabilities were discovered in the context of high-intensity combat.^[22]

There could be other reasons to use a submerged nuclear capability against a vessel, in principle. For example it might be deemed desirable to ‘slime’ a vessel – exposing it to enough radioactive fallout that it could not be easily rotated into port for functions such as vertical launch system (VLS) replenishment unless radiological contamination has been controlled for. Moreover, personnel on a vessel would need to conduct their activities in protective gear, potentially slowing the tempo of action. The Agerholm tests would suggest that ships which maintain a roughly 350 m distance from the detonation point can limit their exposure to fallout. Even so, larger-payload weapons detonating at or close to the surface could have the effect of imposing a requirement for vessel decontamination. Even if this did not remove a vessel from a naval order of battle, it would impose requirements on a fleet which would slow its operational tempo.^[23] A vessel does not necessarily need to be sunk to be prevented from operating effectively.

ASW represents another area where nuclear use may make more sense. Nuclear detonations at greater depths experience less water shock pressure loss from the effects of rarefaction, potentially making nuclear warheads a useful means of engaging submarines as well as other types of underwater target. Weapons comparable to the RUR-5A could be used to prosecute submarine contacts at long distances, as could even heavier payload systems such as the Poseidon. Currently, only one Russian system carries the Poseidon (the special purpose submarine Belgorod) but it could be deployed on other platforms or, indeed, on the seabed.^[24] While it would, of course, also be possible to target a submarine using a conventional torpedo or depth charge within ranges of 1-2 km, the use of a nuclear payload would limit a submarine’s ability to evade a projectile by trying to outrun a munition, using decoys or diving to greater depths.^[25] One of the major challenges with this model was, historically, the fact that the launch platform was itself at risk. This was true for submarines, but also of helicopters, with the Soviets estimating that the likelihood of a helicopter which launched a nuclear depth charge surviving was about 50%. Uncrewed systems could, in principle, obviate this challenge to an extent if they are capable of sufficiently heavy lift.^[26]

There are additional functions that nuclear weapons might play in the subsurface environment. For example, they might be used to disable the sensors which comprise networks such as IUSS. Indeed, the use of nuclear weapons in this capacity represented a major component of Soviet planning for a war with NATO.^[27] Area effects against fixed arrays of hydrophones are likely to be considerably easier to achieve than the targeting of mobile surface groups and would likely form one part of a layered effort to disrupt Western situational awareness at sea.

This could have crucial knock-on effects for the conduct of surface warfare. Should networks such as IUSS cease to be effective and if area effects can be delivered against at least some Western submarines at reach, then the already stretched Western ASW forces would find it even more difficult to operate at scale. This, in turn, could enable Russia’s attack submarines and guided missile attack submarines (SSGNs) to operate with greater freedom – particularly if Allied ASW capabilities are stretched thin by the allocation of US capabilities to the Indo-Pacific, and in the context of a forecast trough in SSN numbers beginning in the late 2020s. The latter is due to the US Navy’s relative decrease in SSN procurement levels during the 1990s, and Los Angeles class SSNs being slated for retirement at a faster rate than their replacement Virginia class SSNs are entering service.^[28]

Deterrence at sea and from the sea

Ultimately, the nuclear threat at sea should be contextualised but not entirely downplayed. It is likely the case that an opponent such as Russia cannot entirely compensate for its targeting weaknesses by using nuclear weapons as an area effect capability. Nonetheless, the use of nuclear capabilities at sea can considerably complicate the employment of naval vessels and could be particularly consequential in the subsurface competition.

This is of considerable concern if, as is often stated, Western nations view their relative advantages in the subsurface competition as a key and enduring advantage. This perceived advantage is already stretched thin by the inherent difficulties in scaling the existing western approach to ASW which will be compounded by geopolitical shifts that will spread US capabilities thin. Adversary nuclear use at sea will exacerbate these challenges and add a new dimension to any conflict with Russia – one in which nuclear weapons have been used against strategic capabilities such as SSNs and hydrophone networks but no civilians have been killed.

While Western policy has historically favoured drawing no distinction between various forms of nuclear use, it is unclear that this is tenable. In practice a degree of flexibility is likely to be needed to deliver response options that are calibrated and proportionate to the provocation at hand. Developing additional low-yield nuclear weapons such as the US’ nuclear submarine-launched cruise missile (SLCM) could represent one avenue.^[29] However, the use of these capabilities is complicated by two factors. First, they would likely have to be used against an opponent’s homeland for a provocation which occurred at sea – effectively generating a strategic level escalation from a theatre level escalation. Second, it is not obvious what a target of commensurate value would be. Targets such as individual airbases would not be so critical to a Russian war effort that a rational Russian leader might accept their loss as the price of a successful maritime campaign which could have strategic ramifications. By contrast, targets such as command centres or the large scale targeting of military facilities with nonstrategic nuclear weapons raise the prospect of strategic escalation.

One avenue might be the forward positioning of nuclear-powered ballistic missile submarines (SSBNs). This approach (which is likely a necessity for British and French SSBNs in any case) would mirror Thomas Schelling’s strategy of reducing one’s own options in an imagined game of chicken. In this metaphor, one side consciously removes its own options so as to deter an opponent who might calculate that if the other has the option to back down, they will. This can be analogised to cutting one’s own brakes in a game of chicken and informing an opponent that this is the case.^[30] If allies forward-positioned SSBNs, they would have no choice but to treat any Russian provocation at sea as strategic by definition, irrespective of its scale, and this very fact might deter Russia from presuming that nuclear escalation could be controlled. However, such an approach also means that events cannot be easily controlled – that very fact makes this deterrent credible but also makes it fraught with risk.

An alternative approach might rely on conventional counterforce capabilities. While it is true that nuclear strikes on strategic targets within Russia would likely precipitate uncontrollable escalation, the ability to engage strategic targets with conventional systems in a limited way might not. This was the basis of allied maritime planning in the 1980s, which would have seen SSNs used to strike Soviet SSBNs. In a contemporary context, conventional prompt strike capabilities might be used in a comparable way to demonstrate an ability to engage targets such as command centres or nuclear storage sites with conventional means.^[31] That the alliance might be able to do this without risking an all-out nuclear war has been a pervasive Russian fear, which could be used to deter Russian nuclear use at sea. This would require considerable capability investments which are, however, beyond the remit of this article.

In sum then, the impact of nuclear weapons at sea should neither be overstated nor ignored. While they are not transformative across the board, they can change maritime dynamics in important ways which makes deterring their use critical.

Sidharth Kaushal

[1] Wayne Hughes, Robert Girrer. Fleet Tactics and Naval Operations. (Annapolis: Naval Institute Press, 2018) p.142

[2] Norman Polmar. Atomic Fist. USNI Proceedings. https://www.usni.org/magazines/naval-history-magazine/2006/august/atomic-fish. Accessed on 05/02/2024

[3] Desmond Ball. Nuclear Weapons at Sea. International Security Volume 10, No 3 (1985-86) : 3-31

[4] The Fundamentals of the State Policy of the Russian Federation in the Field of Naval Operations for the Period Until 2030 Translated by U.S Naval War College. (Annapolis: U.S Naval War College, 2017) p.16

[5] Sidharth Kaushal et al. The Balance of Power Between NATO and Russia in the Arctic and High North. (London: RUSI, 2022) p.45-50

[6] Ibid

[7] Kaushal et al. The Balance of Power Between NATO and Russia in the Arctic and High North Ch 2, 4

[8] Alva Bowen, Ronald O’Rourke. DDG-51 and the Future Surface Navy. USNI Proceedings. 1985. https://www.usni.org/magazines/proceedings/1985/may/ddg-51-and-future-surface-navy

[9] Thomas Newdick. No, The F-35B Does Not Use Afterburner In Vertical Landing Mode. The Warzone. December 27, 2023. https://www.twz.com/no-the-f-35b-does-not-use-afterburner-in-vertical-landing-mode

[10] Bureau of Ships Group Technical Inspection Report: The Effects of Air Blast on Superstructure Reproduced and released in redacted form by the Atomic Energy Commission. (Washington DC: Atomic Energy Commission, 1997) p.7

[11] GlobalSecurity. SS-N-16 Stallion. Globalsecurity. https://www.globalsecurity.org/military/world/russia/ss-n-16.htm

[12] Eric Hagt, Matthew Durnin. China’s Antiship Ballistic Missile: Development and Missing Links. Naval War College Review (2006):87-115 p.92

[13]; A rough calculation based on the online tool Nukemaps which, though not perfectly precise, has been used to inform peer reviewed research before. See Jagnath Sankaran. Pakistan’s Battlefield Nuclear Policy: A Risky Solution to an Exaggerated Threat. International Security. Volume 39, No 3 (2014/15):118-151

[14] On shipboard air defences see Bryan Clark et al. American Sea Power at a Crossroads: A Plan to Restore the US Navy’s Maritime Advantage. (Washington DC: Hudson Institute, 2020) p.27

[15] Sidharth Kaushal, Matthew Harries. Russias Options for Theatre Missile Coercion. RUSI. 19 June 2023. https://rusi.org/explore-our-research/publications/commentary/russias-options-theatre-missile-coercion. Accessed on 01/02/2024

[16] Samuel Glasstone and Philip. J. Dolan. The Effect of Nuclear Weapons.(Washington DC: Department of Defense, 1977) https://atomicarchive.com/resources/documents/effects/glasstone-dolan/index.html

[17] Kyle Mizokami. Tactical Nuclear Weapons at Sea. USNI Proceedings. August 2020. https://www.usni.org/magazines/proceedings/2020/august/tactical-nuclear-weapons-sea. Accessed on 05/02/2024

[18] On the Poseidon see HI Sutton. Russia’s New Poseidon Super Weapon: What You Need to Know. Naval News. 03 March 2022. https://www.navalnews.com/naval-news/2022/03/russias-new-poseidon-super-weapon-what-you-need-to-know/. Accessed on 05/02/2024

[19] On the theory and practice of ASW see Bryan Clark et al. Sustaining the Undersea Advantage: Disrupting Anti-Submarine Warfare Using Autonomous Systems. (Washington DC:Hudson Institute, 2022)

[20] Samuel Glasstone and Philip. J. Dolan. The Effect of Nuclear Weapons.(Washington DC: Department of Defense, 1977) https://atomicarchive.com/resources/documents/effects/glasstone-dolan/index.html

[21] Peter Lobner. 1962 Nuclear Test in the Pacific Near San Diego. The Lycean Group of San Diego. https://lynceans.org/all-posts/1962-nuclear-test-in-the-pacific-near-san-diego/. Accessed on 15/02/2024

[22] Federation of American Scientists. MK-48 Torpedo. https://man.fas.org/dod-101/sys/ship/weaps/mk-48.htm. Accessed on 20/02/2024

[23] Adam.C.Resnik, Steven A Knapp. Developing Navy Capability to Recover Forces in Chemical, Biological, and Radiological Hazard Environments. (Santa Monica:RAND, 2013)

[24] HI Sutton. Video Suggests Russia’s Poseidon Nuclear-Powered Drone Has A Seabed-Launched Version. Forbes. November 17, 2019. https://www.forbes.com/sites/hisutton/2019/11/17/video-suggests-russias-poseidon-nuclear-powered-drone-has-a-seabed-launched-version/?sh=75e702a45b6c. accessed 10/01/2024

[25] On decoys see Michael Peck. New Anti-Torpedo Decoys Could Give U.S. Navy Submarines A Fighting Chance Against Russia or China. The National Interest. February 3 2020. https://nationalinterest.org/blog/buzz/new-anti-torpedo-decoys-could-give-us-navy-submarines-fighting-chance-against-russia-or. Accessed on 13/02/2024

[26] As an example of an uncrewed vertical lift solution see Navy Lookout. PROTEUS – developing an uncrewed helicopter for the Royal Navy. Navy Lookout. October 3, 2023. https://www.navylookout.com/proteus-developing-an-uncrewed-helicopter-for-the-royal-navy/. Accessed on 13/02/2024

[27] Vladimir Samoylov. An Operation to Destroy Enemy Anti-Submarine Forces. Military Thought.1983. https://www.cia.gov/readingroom/docs/DOC_0001431538.pdf. Accessed on 25/01/2024

[28] Navy Virginia-Class Submarine Program and AUKUS Submarine Proposal: Background and Issues for Congress. (Washington DC: Congressional Research Service, 2024)

[29] Nuclear-Armed Sea-Launched Cruise Missile (SLCM-N). (Washington DC: Congressional Research Service, 2022)

[30] Thomas Schelling. Strategy of Conflict. (Harvard University Press. 1960) p. 54

[31] Sidharth Kaushal, Rene Balletta. An Asymmetrical Approach to the Use of Maritime Forces in Competing with Russia. (London:RUSI, 2024)