On the surface, NATO Nuclear Sharing arrangements play a negligible role in the nuclear security of the independently nuclear armed United Kingdom but there’s more to it.

At first glimpse the programme is designed to offer extended deterrence to non-nuclear armed Alliance members, with the UK seemingly able to ensure its own nuclear security through its unilateral Trident system. But Nuclear Sharing plays a key role in the security of the entire Alliance, including the UK.

The programme involves the United States stationing tactical nuclear weapons (specifically air-delivered gravity bombs) in the territory of various non-nuclear armed European allies which are responsible for delivering the weapons in the event of their hypothetical use. Of interest though is that despite the maintenance of an independent British nuclear deterrent, the Nuclear Sharing programme has been essential for British nuclear security since the sweeping reforms to Western nuclear weapons postures after the end of the Cold War.

In 1999 NATO unveiled a new Strategic Concept which exclaimed that “[the Alliance]’s ability to defuse a crisis through diplomatic and other means or… to mount a successful conventional defence has significantly improved”. In line with this new confidence after the demise of the USSR, the Alliance implemented radical changes to its nuclear policy.

Overall nuclear stocks both strategic and tactical were dramatically reduced. All US and UK nuclear artillery and surface based tactical nuclear weapons were withdrawn from the European continent, leaving the US air-delivered gravity bombs as part of Nuclear Sharing arrangements as the only remaining tactical nuclear presence under NATO auspices. As part of this, the UK decommissioned all surface-vessel and air launched weapons – effectively yielding its nuclear triad.

It is because of this British withdrawal of all tactical nuclear weapons after the end of the Cold War that Nuclear Sharing has become so important to not just wider European nuclear security but also British nuclear security. Although British Trident missiles are capable of carrying small-yield warheads, the system remains nonetheless a principally strategic one and the number of warheads with a yield which could be considered sub-strategic is believed to be very low. It is this lack of a real tactical element to the British nuclear deterrent which makes Nuclear Sharing so important to British security.

The British reliance on NATO Nuclear Sharing arrangements is evident when one considers the decision making policy makers and those with their fingers on the button would be faced with in the event of a potential nuclear exchange. Owing to the assurance of mutual destruction and thus the total irrationality of a strategic retaliatory strike against a nuclear armed aggressor which possesses a second-strike capability, any hypothetical use or threat to use nuclear weapons first by NATO to respond to or deter a non-nuclear attack would plausibly be limited to a tactical strike. This means that the retention of tactical nuclear weapons, and therefore by default NATO Nuclear Sharing, is key to the maintenance of credibility to NATO nuclear deterrence and in turn to British nuclear security.

This has been true since the widespread withdrawal of NATO (specifically British) artillery and land based tactical nuclear weapons since the end of the Cold War, with Nuclear Sharing arrangements maintaining the only NATO tactical nuclear presence in Europe. Essentially, Nuclear Sharing exists and will continue to be necessary so long as the Alliance retains the right to First Use and a de facto posture of Flexible Response.

But even if the Alliance and its nuclear members like Britain were to adopt a No First Use policy, Nuclear Sharing arrangements would likely continue or at the very least some other form of tactical nuclear deterrence in Europe would be necessary to maintain European and British nuclear security. This is because tactical weapons are logically not only necessary to ensure that ambiguous threats of First Use are a credible deterrent to conventional invasion, but are also required to maintain a credible deterrent to nuclear attack. Strategic weapons alone cannot conceivably be a credible deterrent to a nuclear attack. If the Alliance unilaterally disarmed itself of all tactical weapons, it would possess less means to credibly respond to and thus deter in the first place a tactical nuclear attack, as it is not credible that the Alliance or any actor would respond to a tactical strike with a weapon of strategic yield, thus escalating a conflict.

As long as the Russian Federation possesses tactical nuclear weapons, it is only logical to assume that NATO should retain its own tactical weapons, in this case in the form of Nuclear Sharing, lest the Alliance be perceived to be self-deterred by the prospect of initiating a full scale strategic nuclear exchange. Essentially, a programme of tactical weapons in the form of Nuclear Sharing or similar can (and likely would) remain even if NATO or its individual members embraced NFU, but First Use ambiguity cannot exist credibly without tactical weapons.

David S. Yost has addressed and convincingly criticised arguments that extended nuclear deterrence could potentially be provided by the UK and France without the need for US tactical weapons provided by Nuclear Sharing, highlighting the fact that British and French nuclear arms are not sufficient in size to provide the psychological comfort necessary to placate the concerns of non-nuclear allies. But in terms of real nuclear security, what is particularly important to bear in mind here is the composition of, and the role played by, the nuclear weapons programmes of these two European nuclear powers. Although it is possible that British Trident missiles are capable of carrying small-yield warheads, the system remains nonetheless a principally strategic one.

This is significant when considering the aforementioned point on the necessity of arms of both a tactical and strategic yield in providing credibility to not only the ambiguity of nuclear First Use deterrence but to nuclear deterrence in general. In regards to France, Paris’ continued operation of an independent deterrent outside NATO auspices and its refusal to fully partake in the decision making processes of the NATO Nuclear Planning Group would no doubt not only cause non-nuclear allies to question France’s commitment to Alliance wide extended deterrence should it assume such a responsibility, but would also hamper the credibility of the wider Alliance’s deterrent.

Of course hypothetically if NATO embraced a policy of No First Use and Russia agreed to totally disarm itself of tactical nuclear weapons (of which it possesses a far higher number than NATO) in a reductions agreement then the need for Nuclear Sharing to underpin the credibility of general nuclear deterrence would abate and the withdrawal of US weapons from Europe would be possible.

But the central role Nuclear Sharing plays in providing credibility and utility to nuclear First Use ambiguity means that for as long as the Alliance (or at the very least certain members within it) believes that nuclear weapons hold deterrent value to non-nuclear attack, and as long as Moscow sustains its retention of vast tactical nuclear weapons stocks, such an event is unlikely and Nuclear Sharing will continue to play a central role in Europe’s and indeed Britain’s nuclear security.