Britain’s Deterrent and the ‘Moscow Criterion’

Improved missile defences could prompt Britain to reassess its deterrent capabilities and have done so historically. As a result of Britain’s current economic and political constraints on its nuclear deterrent, the UK should abandon its periodic obsession with the “Moscow criterion.”

Current UK nuclear weapons policy aims to provide an independent, minimum and credible deterrent. While these parameters have never officially been precisely defined and have shifted over time, the ability to strike Moscow with relative certainty (the “Moscow criterion”) became the dominant benchmark in policy circles for what the UK should be able to achieve on its own in the 1960s and 70s. This was particularly important when it came to upgrading Polaris (Britain’s first submarine-launched, nuclear-armed ballistic missile system, purchased from the United States) which was perceived to be vulnerable to the nuclear warhead-equipped Russian A-35 ABMs. To overcome Soviet ABM systems, the Americans planned to ‘saturate’ the Moscow area with warheads. However, as only one nuclear armed British submarine could be reasonably assured to be on active deployment at any given moment, the UK’s independent ability to strike Moscow was not assured with such a limited arsenal even after the limitations imposed by the 1972 ABM treaty. Such concerns led to the development of Chevaline, which improved Polaris missiles’ penetrative capabilities. However, the programme was exorbitantly expensive, costing £1 billion in 1980, and was kept secret from Parliament by successive Conservative and Labour governments. The mismanagement of this indigenous programme was one of the decisive factors leading to the UK’s adoption of the US-developed Trident system.

While Trident’s improved capabilities and the end of the Cold War temporarily alleviated ABM concerns, the US withdrawal from the ABM treaty in 2002 and deteriorating relations between Russia and the West have resurrected the issue. Free from treaty limitations, Russia has since undertaken a range of programmes to modernise and diversify its missile defences and radar stations. New interceptors include the already deployed S-400 and soon to be finalised S-500 and potentially nuclear-tipped A-235. Although the number of systems that will be deployed will be constrained by financial concerns (the reduction of T-14 Armata tank orders is indicative), a number of advanced defences may be deployed around important sites, such as command and control centres in Moscow. British concern over definitively reaching the “Moscow criterion” may be reintroduced by advanced defences in small numbers, whereas they are unlikely to pose a considerable challenge to the US arsenal. Presently, only 40 warheads and 8 operational missiles are aboard each British Vanguard-class submarine, 120 warheads are held operationally available and the total inventory of warheads is set to be reduced to 180 “by the mid-2020s.”

In terms of offense retaining primacy in response to improved ABM defences, a nuclear force could be expected to follow three general approaches. Since the introduction of MIRVs (Multiple Independently targetable Re-entry Vehicles), the cost-exchange ratio between incoming warheads and interceptors has invariably favoured the attacker. Therefore, one method of overcoming defences is to increase the size of the nuclear arsenal available to be deployed. A similar approach would be to diversify the means of delivering warheads, (e.g. Russia’s new nuclear torpedo or nuclear-powered cruise missile) in an attempt to circumvent missile defences. An alternative approach, which could potentially already be underway, would be to upgrade an existing system with increased penetrative capabilities, as exemplified by Chevaline. This could incorporate upgrading the Trident system with Manoeuvrable Re-entry Vehicles as the French have reportedly done with their new M51 SLBMs.

However, all three approaches would prove problematic for the UK to undertake. Increasing the size of the UK arsenal would contradict current government policy towards the Non-Proliferation Treaty, where incremental decreases in the size of the arsenal are presented as evidence of compliance with Article VI (pursuing nuclear disarmament negotiations in good faith). Likewise, adding new means of delivering nuclear warheads would be heavily criticised by both the international ban treaty movement and be exploited by domestic opposition from both Corbyn’s Labour party and the SNP. Alternatives to submarine launched ballistic missiles in a 2013 government review were largely rejected on the grounds of deterrence credibility and their potential addition as complementary systems was not even considered. Even indigenous upgrades to existing systems to improve ABM penetration, as Chevaline proved, would also be highly expensive. Financial considerations already bear heavily on UK nuclear decision making: the need to deliver “value for money” is a pressing concern. The cost of maintaining Britain’s aging nuclear capabilities, with separate warhead and missile life extension programmes, as well as new Dreadnought submarines, already presents costs of around £4.5 billion this financial year.

Without the near-term prospects of a new arms control treaty, Russia’s own financial constraints may save Britain from dealing with this dilemma. Nevertheless, a credible ABM system around Moscow may re-invite evaluation of the purpose and viability of the UK’s deterrent. A lower threshold of certainty for striking well-defended targets may be unavoidable, as economic and political considerations would make any move to expand or add capabilities to the nuclear arsenal highly challenging. One solution would be to become further reliant on US technical developments, but this would not be cost-free, and cooperation could become increasingly uncertain in an age of ‘America First’. Beyond abandonment of Trident or the notion of nuclear independence, a further alternative would be to reject the “Moscow criterion” altogether, expand target selection, and further reflect upon the limitations of minimum deterrence in an age of increasingly potent ABM systems.​

Geoffrey Chapman is a PhD candidate and research assistant at the Centre for Science and Security Studies at King’s College London. His thesis is on the institutional development of Britain’s nuclear weapons programme and he writes on other CBRN issues.

Image credit: Nuclear submarine HMS Vanguard arrives back at HM Naval Base Clyde, Faslane, Scotland following a patrol, Wikimedia commons.