Reducing Britain's nuclear capability would be a grave mistake | David Blagden

Cutting the number of nuclear submarines will prevent Britain keeping one at sea, which is essential to deterring aggressors

The Cabinet Office will this month publish its review into alternatives to like-for-like replacement of the UK’s Trident nuclear deterrent – or, more specifically, the Vanguard class of Royal Navy submarines that currently carries the Trident D5 ballistic missile. While the review will shy away from making firm policy choices (for intra-coalition political reasons), we know that alternatives to a replacement Trident system will be presented as “compelling” options, but exposed as both less capable and more costly, and therefore unlikely to be pursued.

The move towards a reduced deterrent posture, however, is likely to come in the form of a suggestion that only building two or three boats in the new Trident-carrying submarine class would be a plausible option – a concession dear to senior Liberal Democrat defence figures, and one that may be tempting to other leaders in search of savings – in the place of the four outgoing Vanguards. Such a choice would be a grave mistake. Regardless of where one sits on the left/right political spectrum, if Britain is to possess a nuclear arsenal at all – as all three of the major parties still think we should – then it must be configured to promote caution rather than aggression in international crises.

Moving from four ballistic missile submarines (SSBNs) to only two or three would end the Royal Navy’s ability to keep one boat of the class permanently deployed at sea, as the then First Sea Lord made clear in 2009. This posture – known as continuous at-sea deterrence, or “kaz-dee” (CASD) – has been maintained without interruption since 1968. The rationale behind CASD is that if at least one submarine is always deployed, then Britain’s ability to retaliate against nuclear aggression would be assured even if the UK – including the Royal Navy’s bases – was attacked with little or no warning. In short, a continually-deployed SSBN provides a “secure second-strike” retaliatory capability.

The great thing about secure second-strike nuclear arsenals is that they stop there being rewards for aggression, thereby helping to stabilise international diplomatic and military crises. An opponent does not have an incentive to strike you first, because doing so does not diminish your ability to inflict devastating retaliation – a potent deterrent to potential aggressors. A submarine tied up alongside HM Naval Base Clyde, by contrast, is not a deterrent – it’s a “target”. A potential aggressor contemplating an attack on Britain would face powerful incentives to destroy it before it left port.

Faced with this reality, the government would have a terrible choice to make at the beginning of any international dispute with another nuclear power. Do they send the submarine to sea, a tremendously escalatory move that would turn a mere dispute into an …read more