Earlier this year, the Bulletin of the Atomic Scientists' Science and Security Board announced their decision to move the Doomsday Clock closer to midnight. Around the same time, the US Department of Defense released the 2018 Nuclear Posture Review (NPR) – these two developments draw from the same global security environment but are in stark contrast to each other in the faith they place in nuclear weapons. Amongst a slew of modernisation measures that the new NPR proposes, two stand out: development of low-yield nuclear warheads and an expansion of the scope of nuclear weapons use by the US against an adversary.

According to the new NPR, the US plans to deploy “low-yield sea-launched ballistic missile nuclear (SLBM) warheads” and re-commission a “modern nuclear armed sea-launched cruise missile (SLCM)," again with a low-yield nuclear option. Introducing a low yield nuclear option is a form of ‘tailored deterrence’ that the US has been contemplating for quite some time now, especially vis-à-vis Russia. Russia has been known to allegedly lower the nuclear threshold by increasing its repository of non-strategic nuclear weapons, also commonly known as tactical nuclear weapons, thus bringing back US concerns about limited nuclear use. Russia currently possesses 4,500 nuclear warheads of which 2,000 are believed to be non-strategic.

Quoting Russia’s modernisation drive as one of the primary reasons for US policy change, this move is likely to close the gap between Russian and US nuclear capabilities in terms of their non-strategic nuclear weapons. However, it can be considered militarily inexplicable for one important reason. Russia’s decision to modernise its military with non-strategic nuclear weapons was to compensate for its lacking conventional military strength, in which domain the US is far superior. Even at present, the US remains far ahead of Russia in the conventional military capabilities domain.

The rationale behind US deployment of a low-yield nuclear option as mentioned in the NPR hinges on its so-called ability to contain a possible limited nuclear escalation by countries like Russia. However, escalation control only makes for a credible theoretical framework and has slim chances of any practical implementation. A low-yield, non-strategic nuclear warhead can cause enough damage to invite a full-scale nuclear response.

On the one hand, the NPR document emphasises measures like “decreasing misperception and miscalculation and avoiding destabilising nuclear arms competition,” while at the same time proposing the re-introduction of a nuclear-tipped SLCM (which was decommissioned in 2011) in the long-term. This is likely to increase the chances of an accidental cataclysmic nuclear exchange precisely because of the ability of a cruise missile to disable any interception or detection, leading to potential miscommunication between two adversaries.

The NPR text also expands the circumstances that can lead to a possible use of nuclear weapons by the US against an adversary by introducing a new and rather ambiguous category of "non-nuclear strategic attacks." This could include a host of possibilities from cyber warfare, conventional attacks on civilian population and infrastructure, to a chemical or biological weapons attack. The text goes on to say that “It remains the policy of the United States to retain some ambiguity regarding the precise circumstances that might lead to a US nuclear response.”

Employing ambiguity in a country's nuclear doctrine is not new; the French nuclear doctrine, for example, maintains vagueness as to what constitutes ‘national interests’. Nonetheless, lack of transparency in explicitly stating the circumstances that would lead to a nuclear strike against an adversary, especially in case of non-strategic nuclear weapons, can create space for a pre-emptive strike from the adversary owing to the uncertainty of possible first strike.

In its definition of the "extreme circumstances" that would invite a nuclear response, the document includes non-nuclear strategic attacks on the US and its allies; even a conventional attack on one of its allies’ strategic infrastructure could qualify for US nuclear first use. This change has to be seen in consonance with the US decision to modernise its Nuclear Command, Control and Communications (NC3) system that facilitates the deployment of a nuclear weapon in times of crisis, thus justifying a nuclear response at the slightest suggestion of even a miscalculated or misinterpreted early warning assessment. This eventuality leads to the question about whether ambiguity, in this particular case, can actually serve to enhance deterrence.

The NPR uses the “uncertain international security environment” and Russia’s muscle-flexing as justifications for significantly modernising its existing nuclear arsenal. Although it claims to be responding to changing strategic necessities, it is also true that as the Doomsday Clock nears midnight, in many ways the NPR carries the potential of doing further disservice to nuclear non-proliferation, and making the global security environment more perilous.

Shivani Singh is a Researcher with the Nuclear Security Programme (NSP) at IPCS.