Like for like renewal of Trident will come at expense of conventional forces

Download PDF(182KB)

The UK's current commitment to maintain a nuclear-armed missile submarine on deterrent patrol at all times (Continuous At-Sea Deterrence, or 'CASD'), is driven as much by institutional and political momentum as by strategic necessity, and plans to order a new generation of submarines after 2015 now threatens to be at the expense of further reduction in conventional forces according to a new report from the Royal United Services Institute (RUSI).

TridentAlthough the UK Government is committed to maintaining an effective nuclear deterrent, Continuous At-Sea Deterrence (CASD): Costs and Alternatives - written by Professor Malcolm Chalmers - makes a strong case for re-examination of whether alternatives to current CASD policy could yield significant financial savings while continuing to meet this agreed objective. Highlighting a 'stark' disconnect between current conventional and nuclear planning, Chalmers argues that fiscal pressures, coupled with the reduced threat of surprise nuclear attack, mean the cost equation of maintaining CASD is now changing.


'There is now a stark gap between the assumptions on which planning for the UK's conventional and nuclear forces, respectively, are based... The current Strategic Defence and Security Review (SDSR) is based on the assumption that a significant threat of attack on the UK homeland by other states will not re-emerge without an extended period of strategic warning. In contrast, the commitment to maintain a nuclear-armed missile submarine on patrol at all times (known as Continuous-At-Sea-Deterrence or CASD) has remained largely unchanged since the 1960's, when a surprise attack on Western Europe by the Soviet Union was a central driver for UK force planning.'

'Given the severe costs that Trident renewal could require... there is now a strong case for a re-examination of whether alternatives to current CASD policy could yield significant financial savings while continuing to meet this agreed objective. The fiscal situation facing the Ministry of Defence (MoD) is significantly worse than was assumed in 2006, when current renewal plans were drawn up by the previous government', writes Chalmers.

With the Treasury insisting that additional costs for Trident renewal be met from the MoD core budget, the effect of this on conventional capabilities will be 'further multiplied' by expected real term cuts in defence spending.

'MoD planners may decide to shift resources out of other areas (such as personnel) in order to help to pay for the increased strain on the equipment budget after 2015. What is clear is that the inclusion of Trident renewal in the core budget, on current plans, could require the MoD to plan for a further significant real reduction in annual conventional spending by 2020, over and above any reduction that the Spending Review decides to make over the next four years.'

In the paper, Professor Chalmers assesses four possible options for maintaining both an effective nuclear deterrent and also reducing costs in light of anticipated budget restrictions. The options include:

1.       A 'Normally-CASD' Submarine Force - Extend the Vanguard-class submarines, delay the start of peak spending on the renewal programme until 2019/2020 and redefine what is meant by 'CASD' to cut the fleet of boats from four to three.

2.       A 'CASD-Capable' Submarine Force - Abandon CASD in normal circumstances, but maintain a credible capability to reconstitute it if required.  This option could cut the fleet of successor submarines from four to two and delay peak spending until 2023/2024.

3.       A 'Dual-Capable' Submarine Force - Rationalise the submarine fleet around a single model of boat, which could be used either for conventional or deterrent roles. This new model would eventually replace both Vanguard and Astute class submarines.

4.       A Non-Deployed Strategic Force - A more radical option, this would abandon the UK's submarine-based nuclear deterrent, maintaining only a non-deployed arsenal. Offering the most substantial financial savings, this option would still aim to provide a guaranteed - but not prompt - ability to retaliate against future nuclear attacks.

To read the paper in full, please visit



1.     For all enquiries please contact Daniel Sherman

2.     A copy of 'Continuous At-Sea Deterrence (CASD): Costs and Alternatives' can be viewed online at

3.     Malcolm Chalmers is Professorial Fellow in British Security Policy at RUSI, as well as Visiting Professor of Defence and Foreign Policy in the Department of War Studies, King's College, London. He was a member of the UK Defence Secretary's Advisory Forum on the 2010 Green Paper 'Adaptability and Partnership'.

  • 4. RUSI is an independent think-tank for defence and security. RUSI is a unique institution; founded in 1831 by the Duke of Wellington, it embodies nearly two centuries of forward thinking, free discussion and careful reflection on defence and security matters.

Explore our related content