Nuclear weapons have returned to prominence. Russia now regularly makes scarcely veiled nuclear threats as part of its war with Ukraine, with many further arguing that Ukraine in giving up nuclear weapons in 1994 helped make itself vulnerable. North Korea has declared itself a nuclear weapon state while acting increasing aggressively towards South Korea, and China is considerably expanding its nuclear weapon stocks while practicing striking Taiwan. This turbulence has downsides but also throws up some new opportunities to be more strategically innovative regarding nuclear weapons.
Modern nuclear thinking remains influenced by last century’s Cold War and, in particular, America’s nuclear plans and structures of that period. At that time, the U.S. was focused on countering the Soviet Union and determined it would provide the high-end nuclear forces the West needed, while assiduously working to ensure the number of states with nuclear weapons stayed minimal.
Belligerent Sanctuaries
Today, the situation is different. The U.S. is now focused on countering China. The Trump administration believes Russia, the successor state to the Soviet Union, can and should be managed by Europe, preferably alone. Importantly, Russia has declared that in the event of an attack that poses a “critical threat to [Russian] sovereignty,” they will respond with nuclear strikes even if the attack only involves non-nuclear weapons (Gabuev, 2024).
Russia began making nuclear threats from February 2022 when the Russian war with Ukraine sharply escalated. These threats lacked credibility as risking major nuclear war by conducting strikes into Western Europe using high-yield strategic nuclear weapons was implausible. U.S. intelligence sources assessed the likelihood of such Russian nuclear weapon use was very low, about 5-10% (Entous, 2025).
Even so, Russia’s nuclear threats are influencing the U.S. and some Western European countries to sharply limit the use of the long range missiles they provide Ukraine. The country is only permitted to undertake strikes at Russian targets located near its border; deeper attacks into Russia are not allowed. Russia’s nuclear threats have created a sanctuary against the more damaging kinds of strikes that Ukraine might undertake (Rachman, 2024).
In future conflicts, nuclear armed powers may be able to threaten the use of nuclear weapon to deter their non-nuclear armed adversary from escalating the conflict geographically. Using such “aggressive sanctuarization,” states can now seemingly avoid serious punishment for their provocative actions (Lozier, 2022). Such states then have a low threshold to start a war but have little incentive to stop. They may continue the war indefinitely.
Beyond the Ukraine war, this situation could reoccur in several hypothetical scenarios including Russian involvement in the Baltic states, a North Korean attack on South Korea, or a Chinese assault on Taiwan. None of these possible target countries have their own nuclear weapons.
Countering Belligerent Sanctuaries
This situation is unlike Cold War scenarios that typically envisaged large scale use of high-yield nuclear weapons in counter-city and counter-force strikes (Freedman, 1989). The threat of using of such weapons to counter aggressive sanctuarization is not credible; the destruction would be vastly disproportionate to the gains. In contrast, low-yield tactical nuclear weapon strikes may be credible and accordingly useful to influence an aggressor’s political leaders to change their calculus.
The yield of a nuclear weapon is the energy that would be released if detonated measured against the weight of TNT required to produce the same amount of energy release. For example, the atomic bomb dropped on Hiroshima had an estimated yield of about 15,000 tonnes of TNT (Ragland, 2022). In the Cold War, large numbers of high-yield weapons of the order of 20,000 tonnes to beyond a million tonnes were constructed. Such high-yield weapons were necessary as their delivery missiles had accuracies measured in tens of kilometres making large miss distances likely. High-yield weapons were so powerful that aiming errors were acceptable.
In contrast, modern missile accuracies are now confidently measured in centimetres, with high probabilities of hitting targets. A modern missile would therefore only require a relatively low-yield nuclear warhead to be highly effective against tactical targets such as command and control facilities, transportation nodes, airfields, amphibious assaults, gasoline stockpiles and munition storage areas. Such nuclear warheads are both feasible and sufficiently lightweight to easily fit into modern missiles or attack drones. Today’s B-61 weapon weighs 300 kg and offers a 300-tonne yield (Kristensen and Norris, 2014). In the Cold War, the very light 30 kg W-54 offered yields between 10 to 1,000 tonnes. In comparison, the largest U.S. conventional bomb currently is the 9,800 kg GBU-43 with an explosive yield of 8.45 tonnes (Rogoway, 2017).
Unlike conventional bombs that use blast and fragmentation, nuclear weapons damage using blast and radiation. A 1,000-tonne airburst would collapse concrete structures out to about 350 metres from the detonation, while the prompt radiation would probably lead to the deaths within 30 days of 50% of people who were within 900 metres, unless they received medical treatment. The residual radiation is less in an airburst than a ground detonation, and in this example would reduce to a safe level after four days (Ragland, 2022).
Consequently, low-yield nuclear weapons in the low kiloton yield range could realistically be used against an invading force. These would make an invasion almost impossible, as the military forces employed would need to disperse widely to avoid being targeted and so not be able to be massed to break through defensive lines, while their logistic resupply would become very difficult.
Accompanying the emergence of aggressive sanctuarization strategies is a more carefree U.S. administration. The current discussions concerning Germany, Poland, and South Korea possibly acquiring nuclear weapons is not receiving the strong U.S. pushback it would have in earlier decades. These discussions are intensifying as doubts about the U.S.’s continued provision of a nuclear shield for its allies in any war, apart from possibly with China, grow. Illustrating this, a senior U.S. Department of Defense Undersecretary in a post retweeted by President Trump argued that U.S.-ally South Korea should defend itself against nuclear-armed North Korea essentially alone, to allow the U.S. to focus on countering China (Kim, 2024).
Acquiring Small Nuclear Weapons
Almost all nations are signatories to the 1968 nuclear non-proliferation treaty (NPT) which allows only five states – the U.S., Russia, China, the U.K. and France – to have nuclear weapons. Under the treaty, all other nations can only use nuclear energy for civilian purposes, such as power generation. The NPT has been largely successful although there are some outliers. Israel, India and Pakistan did not sign the NPT, and North Korea withdrew from it; all subsequently developed nuclear weapons.
Consequently, the countries most in danger from belligerent sanctuary situations — the Baltic states, South Korea, Taiwan, and Ukraine which is already immersed in such a scenario — would need to withdraw from the NPT before beginning national nuclear weapon programs. All would also face political, technical, financial, and timeline difficulties in completing such programs. In that regard, South Korea is considered the U.S. ally most ready to acquire its own nuclear weapons (Tucker, 2025).
An alternative is extended nuclear deterrence (END), which arose in the Cold War as a complement to the NPT. Under END, the U.S. agreed to provide allies with an assurance of nuclear deterrence protection using America’s high-yield strategic nuclear weapons if they didn’t pursue individual national weapons programs. The belligerent sanctuary case is subtly different in that the nuclear weapons involved would be low-yield and much less destructive. The context has also changed as nuclear strikes would generally be more measured and there would be more time to consider them then in the Cold War. Furthermore, relatively few low-yield weapons would be needed to deter or be used in extremis. The weapons are intended to influence the aggressor states’ leadership, not to destroy their country.
The U.S. would technically be able to give an END assurance concerning the use of low-yield nuclear weapons in a belligerent sanctuary case, however, several European countries have recently expressed concern over U.S. reliability and the current administration’s dealings with Russia (Higgins, 2025). The U.S. would need to address such worries if it offered a low-yield nuclear weapon END assurance to the Baltic states. On the other hand, France and the United Kingdom might be able to give such an assurance to the Baltic states and possibly also to Ukraine. Both would probably need to construct low-yield nuclear weapons as their current nuclear weapons are high-yield and designed for strategic deterrence, not tactical employment (Bell and Hoffman, 2025).
In the cases of Taiwan and South Korea, the U.S. appears the only current option. For Taiwan, the U.S.’s steady decoupling from China may eventually allow them to give such an assurance. An END guarantee would be a lower cost option than other deterrent alternatives including the so-called Hellscape asymmetric warfare concept involving the use of very large numbers of unmanned air and sea systems to thwart hostile amphibious assaults (Keller, 2024, August 18). Giving a low-yield nuclear weapon END assurance to South Korea may also be seen as a way to reduce U.S. forces based in the country while still strengthening deterrence against North Korea.
An END guarantee may appear more certain if complemented through using nuclear sharing. The US could possibly share low-yield nuclear weapons with South Korea and the Baltic States; Ukraine and Taiwan would be less likely candidates.
The U.S. has long sharedhigh-yield nuclear weapons with Germany, Belgium, Holland, Italy, and Turkey, although the U.S. retains full control using a dual-key system with the host nations then responsible for delivering the weapons to nearby targets. Mirroring this, Russia has now moved high-yield nuclear weapons into Belarus, apparently also using a dual-key system and with Belarus involved in target selection (Associated Press, 2024).
Whether nuclear sharing meets the NPT is contested (Hayashi, 2021). America argued in the Cold War that the U.S. controls the weapons “unless and until a decision were made to go to war, at which time the treaty would no longer be controlling” (Office of the Historian, 1968). At the time, the Soviet Union did not reject this argument, and the situation in Belarus suggests Russia still thinks similarly.
A further variation on nuclear sharing that was considered during the Cold War is forming a multi-lateral nuclear force made up of nuclear-armed warships or submarines funded and operated by a group of countries. This idea proved unattractive as there was a perceived need to be able to react to pop-up nuclear threats very quickly, perhaps within minutes. A multi-lateral force was seen as being inherently slow to react, as the nations involved would all need to give their approval. In contrast, considering using low-yield nuclear weapons in the envisaged belligerent sanctuary circumstance would generally involve comparatively long decision-making timescales. Moreover, having more nations included in decision-making would make any retaliatory actions by the aggressor state more problematic and costly.
Conclusion
Low-yield nuclear weapons may be a worthwhile counter to the use of belligerent sanctuary strategies by nuclear armed states. However, there are valid concerns that actually using such weapons on the battlefield would break the strong taboo against using nuclear weapons and could lead onto the use of high-yield nuclear weapons. In a sense, this is a bridge that might be left uncrossed until the situation arose.
Today’s question is whether it is sensible to proceed down the path of developing the strategies, doctrines, and means to deploy very low-yield nuclear weapons to deter aggressor states from using belligerent sanctuary strategies. There is no credible way now to achieve this deterrence as threatening to respond using high-yield nuclear weapons is implausible. In contrast, very low-yield nuclear weapons could credibly destroy an invading force that crossed a country’s borders. Such weapons offer a means to deter some of the kinds of aggressive threats and actions presently being confronted.
References:
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The views and opinions expressed in the INSIGHTS publication series are those of the individual contributors and do not necessarily reflect the official policy or position of Rabdan Security & Defense Institute, its affiliated organizations, or any government entity. The content published is intended for informational purposes and reflects the personal perspectives of the authors on various security and defence-related topics.
