Debating the Deterrent: Why the Cruise Missile Option Does Not Add Up

With defence spending under scrutiny, the spotlight has long since shone on Britain's nuclear deterrent. But while the costs of replacing Trident are high, the difficulties of creating a new system may be a price we simply cannot afford to pay.  

By Dr Lee Willett, Head of the Maritime Studies Programme, RUSI

In the build up to the May 2010 General Election, the two opposition parties could not have disagreed more on the issue of the United Kingdom's independent strategic nuclear deterrent. The Conservative Party endorsed the Labour Government's position, as defined in the 2006 Defence White Paper on the deterrent, that the UK's requirement for a minimum deterrent remained unchanged.

The Liberal Democrats' position, on the other hand, was that the UK should examine more cost-effective options other than a like-for-like replacement. This proposal was clearly an ineffectively masked abolitionist position, but nevertheless it successfully re-ignited the debate as to whether cheaper and equally effective deterrent options existed1.

Since the election, the fate of the UK's nuclear deterrent has remained the subject of much discussion, with a submarine-based cruise missile capability most often put forward as the most plausible alternative. However, this analysis will demonstrate why this option will not provide the strategic credibility required to underpin an effective deterrent posture and, crucially, will not prove to be cheaper than the current system.

The Future of the United Kingdom's Nuclear Deterrent: Cost and Cruise Missile Issues in the 2006 White Paper

Despite pre-Election claims from the Liberal Democrats that a like-for-like replacement system would cost as much as £100 billion throughout its life-span, there is no official, publicly-available figure to support this claim. Some constituent costs of the renewal programme were identified in the 2006 White Paper on the deterrent2:

i. £15-20 billion for four new submarines, possible refurbishment or replacement of the warheads, and life-long infrastructure capital costs. The White Paper estimated that the procurement costs would average about 3% of the current defence budget over the main period of expenditure,

ii. An average of £350 million per annum between 2005/06 and 2007/08 spent at Aldermaston, with further investment necessary, and likely to be peaking in the next decade at about 3% of the defence budget,

iii. Through-life costs for the whole programme, once the new boats are in service; likely to be around 5-6% of the defence budget.

While estimating total costs for a programme which will last beyond 2050 is a highly speculative exercise, the White Paper indicated that the Labour Government perceived the broad costs for future developments to be similar to what they are today. The then Secretary of State for Defence, Des Browne MP, stated that when 'considered across the life of the system ... [the cost] amounts to around two tenths of one per cent of our GDP'3. As current Defence Secretary Dr Liam Fox noted recently, 'the capital costs of the successor programme are likely to be up to £20 billion spread over the next decade or so. But that seems to me to be pretty good value when compared with the amount spent every year by Government - over £650 billion annually.'4

The White Paper also set out broad cost issues relating to alternative systems5. However, in relation to a submarine-based cruise missile option, it stated that 'any programme to develop and manufacture a new cruise missile would cost far more than retaining the Trident D5 missile.'6

The Strategic Defence and Security Review

In terms of whether the deterrent should be considered within the Strategic Defence and Security Review (SDSR) announced by Dr Fox on his first day in office, again there was a difference in position between the Conservative and Liberal Democrat parties. The Conservatives had stated originally that the renewal decision and programme issues would not be revisited in the defence review. The Liberal Democrats argued that it would be wholly inappropriate to conduct a defence and security review without considering the deterrent. Given the difficult and emotive financial circumstances and the predicted 10-20% cut in defence spending, the Coalition found a compromise position: to conduct a value for money review of the renewal programme. Under this review, whilst reinforcing the current policy of continuing with a deterrent and renewing the submarine-based capability, the Ministry of Defence (MoD) is running a full examination of the current system. This covers the programme timetable, submarine, missile, missile tube and warhead numbers, infrastructure and other support costs, the industrial supply chain, and finally whether the policy can be met while reducing programme cost, including by shifting the balance between financial savings and operational risk7.

Yet not even this compromise position has drawn a line under the debate. The Guardian stated that Government concerns about the nation's finances were now so acute that Prime Minister David Cameron and Chancellor of the Exchequer George Osborne were now unsure as to whether the UK can afford to renew the deterrent at all, despite arguments that UK security would be fundamentally weakened without it8. Throughout its history as a nuclear power, the UK has repeatedly reviewed its capability options to support a minimum independent strategic deterrent and has concluded time and again that a submarine-based ballistic missile system is the most cost-effective option. However, as the Cabinet Office, MoD and HM Treasury spend the summer mulling over the strategic choices facing the SDSR, the deepening financial concerns have led some to argue that the summer will see the Government re-examining whether cheaper, credible alternatives exist.

Cost Credibility

However, there are some significant issues which need to be understood in relation to funding alternative options to the current deterrent system. This is particularly the case when considering a submarine-launched cruise missile.

Firstly, the national strategic deterrent is a political asset for the UK which is currently funded separately from the defence budget9. With defence facing real term budget cuts of up to 20 per cent over the next four years, it seems implausible that cancelling the deterrent or switching to an alternative system would see any potential savings added to the defence budget for spending on conventional systems. Moreover, any savings which could be made by cancelling or changing the programme would not be realised until the next Parliament and beyond, up until the 2040s, which is when the vast majority of spending on the renewal programme will occur. Furthermore, there is the matter of the significant costs of decommissioning the current system and its infrastructure, costs which are not yet fully understood because it is not yet clear how to fully and safely decommission military nuclear programmes.

Secondly, a cruise missile system, especially a submarine-based one which neither the United States nor France are developing themselves, would be a new system for the UK, requiring significant new technological developments. Such a system would also require investment in new infrastructure, as the infrastructure required to support a cruise missile rather than a ballistic missile would be fundamentally different. Developing a new system and infrastructure autonomously would require significant research and development spending, especially at the early stage in the programme; precisely the time when the UK has no funding for significant new capital projects. With the infrastructure for a ballistic missile capability already in place and largely paid for, the significant spending on the submarine-launched ballistic missile option would not begin until beyond 2014. A new cruise missile programme, however, with all the upfront investment required, would have a spending profile wholly converse to both the existing programme and to the Government's plans to reduce spending significantly within the next four years.

Thirdly, the US has a number of nuclear-armed Tomahawk cruise missiles which, having been held ashore in non-operational storage since the end of the Cold War, are now to be retired under the 2010 Nuclear Posture Review (NPR). These missiles represent the only option for the UK to buy a long-range cruise missile 'off the shelf'. Furthermore, the development of a cruise missile system would also violate the Non-Proliferation Treaty (NPT) as well as cloud the spirit of the Obama-led push towards a multinational-focused global zero. Moreover,  a US decision to lend or sell nuclear Tomahawks to the UK would be in violation of the US' own commitment both to the NPT and to the Missile Technology Control Regime (MTCR). In the highly unlikely event of the US agreeing to such an option, it might yet be forced to withdraw under the NPR; leaving the UK to bear the support cost burden itself.

Finally, assuming that the US had no desire or ability to share its nuclear Tomahawk cruise missiles with the UK, the latter would be faced with developing and paying for a new cruise missile, nuclear warhead and supporting infrastructure, alongside addressing a raft of safety legislation which would be borne out of the development of a new system. The costs of so doing would be astronomical.

Strategic Credibility

The current submarine-based ballistic missile strategic deterrent system exists, at any one time, as a single, survivable submarine with sufficient missiles and warheads onboard to address any security threat it encounters. It can launch its missiles from any position, up through UK or international airspace, outside the atmosphere and down into the airspace of the target country. The missiles travel at hypersonic speeds to a distance of up to 7,500 miles.

Currently, there is no long-range, hypersonic cruise missile. The only alternative is the US nuclear Tomahawk. As noted above, in the wake of the NPR the US will be deploying only conventional Tomahawk variants. The conventional Tomahawk has a range of up to 1500 miles, and even given the slightly longer range of a nuclear Tomahawk (being slightly lighter than its 1,000 lb conventional counterpart), this range is arguably insufficient to support a strategic deterrent role. A cruise missile like Tomahawk also flies at around 500 miles per hour, through the earth's atmosphere.

The technical capabilities of a ballistic missile and a cruise missile are therefore very different. In terms of the UK's requirement for its strategic deterrent, the distinctions would have the following significant consequences.

i. A submarine firing a shorter-range weapon would need to be further 'up threat' i.e., nearer the target , rather than remaining in more secure home or local waters. This would significantly increase the risk to the vessel.

ii. Strategic risk is also created by the fact that the UK would potentially be deploying conventional and nuclear versions of the same missile. The consequence of this would be that any potential opponent, on detecting what might in fact be the launch of only a conventional missile, might assume that a nuclear weapon had been fired and react accordingly. It was for this very reason that the US stood down its nuclear Tomahawks. The UK's possession of both nuclear and conventional cruise missiles might also create a risk that a conventional Tomahawk launch from a US submarine would be interpreted as a UK nuclear strike.

iii. As cruise missiles travel through the earth's atmosphere rather than above it, a missile carrying a nuclear warhead might on occasion need to pass through the airspace of a third party state. It seems unlikely that permission for such a transit would be granted by the state in question

iv. A cruise missile travels at 500 miles per hour; a cruising speed for a fighter aircraft. In testing the UK's Tomahawk and Storm Shadow (air launched) conventional cruise missiles, missiles are followed and monitored in flight by chase planes. In sum, this means that a missile could be shot down by a fighter aircraft. Operations since DESERT STORM in 1991 have shown that, in certain circumstances, cruise missiles can also be shot down by anti-aircraft systems. This suggests that a much larger number of missiles and warheads would be required to ensure sufficient penetration of any quality of defensive system. Such a decision would be unwelcome at a time when the political focus is very much on the UK reducing its nuclear inventory and when the desire to reduce global nuclear force levels is breathing new life into the international disarmament agenda.

v. The UK's dependence on the US to supply core elements of its current programme - namely the Trident ballistic missile (the submarine itself retains operational independence) - has stimulated significant debate as to whether the UK is too closely tied to the US on this issue. Unlike a ballistic missile (which relies upon its physical ballistic trajectory and a latitudinal start and end point to reach its target), a cruise missile - because of its method of propulsion, mode of flight and smaller punch - relies on more refined targeting data and guidance systems. The UK relies on the US for targeting data for its conventional cruise missile operations. It is likely that the use of a nuclear Tomahawk would see increasing dependence on the US for operational targeting data.

vi. Operational experience has also shown that Tomahawks occasionally stray from their planned flight path, for various reasons: the consequence of this is that the missiles run on, off course, until they run out of fuel and land (without detonating) on the ground10. As a result, there would be the risk that a UK nuclear missile could land in the territory of a third-party state.

vii. As the cruise missile warhead is smaller than the Trident warhead and can only carry one warhead (a Trident missile can carry multiple warheads), more missiles and more submarines would be needed to retain the current level of deterrence. For example, the UK's current deterrent posture is based around one submarine deployed permanently at sea carrying up to 48 warheads. The ASTUTE-class attack submarine (SSN) is seen as the likely basing option for a nuclear cruise missile rather than a replacement for the current VANGUARD-class ballistic missile submarine (SSBN). However, an ASTUTE class SSN carries less than 40 weapons, and this number would include torpedoes and conventional cruise missiles. Thus, at least two submarines would be needed to carry out the same deterrent task. The UK is at the moment committed to building only seven ASTUTE-class SSNs: seven ASTUTES would be enough to allow the UK to commit two boats permanently to the deterrent role whilst carrying out all the other global tasks required of its SSN flotilla11. Putting nuclear weapons onboard a platform which also has a conventional role, would create political and military risks relating to the conventional role of those SSNs. For example, other nations (whether hostile or friendly) might be forced to conclude that a UK SSN operating in their region would be carrying nuclear weapons. Furthermore, ASTUTE boats are not designed or certified to carry nuclear weapons. The UK's stringent safety case criteria would dictate significant and costly design changes to the boats.

viii. In terms of developing new capabilities, at a national level the UK has stated a desire to retain the sovereign ability to develop its own nuclear warhead. Relying on another nation to provide this capability would compromise this sovereignty.


In terms of an air-launched cruise missile capability, the attendant problems of designing a new missile and warhead persist. A Tomahawk missile is not designed to be deployed on aircraft, although some consideration has been given in the past to fitting Tomahawks in rotary launch canisters used to transport aircraft. The US and France do have air-launched nuclear programmes, but the UK does not currently have any aircraft which could support the weapons.

The US is considering developing a new strategic bomber, but such an aircraft will not be available until the 2040s and it is not yet known if it will be nuclear-capable. Once again, an air-launched cruise missile option would leave the UK facing the bill for developing the elements of such a programme from scratch. Moreover, an air-launched capability will need an air base in the UK as its home. The UK would be faced with the choice of having to keep nuclear-armed aircraft permanently in the air (where they would still be visible) or risk having the air base - and its neighbouring community - as the target for a nuclear strike by a potential adversary.



Dr Willett wrote his doctoral thesis on the Tomahawk Sea-Launched Cruise Missile (Cruise Control: the Tomahawk Sea-Launched Cruise Missile and the Effects of the Collapse of Communism upon US-Soviet Strategic Arms Policies and upon US-Soviet Strategic Arms Control, Department of War Studies, King's College, London, May 1997).


1 See, for example: Lord Gurthrie The defence of Britain: what can we do? Speech made at the Centre for Policy Studies, 10 March 2010. Available on-line at

2 Ministry of Defence (MoD). (2006). The Future of the United Kingdom's Nuclear Deterrent. Command (Cm) 6994. Presented to Parliament by the Secretary of State for Defence and the Secretary of State for Commonwealth and Foreign Affairs, By Command of Her Majesty, December 2006. Norwich: The Stationery Office (TSO). pp.26-27, paras 5-11 to 5-14.

3 Browne, D. 'The United Kingdom's Nuclear Deterrent in the 21st Century'. Speech at King's College, London, 25 January 2007.

4 Rt Hon Dr Liam Fox MP. 'Deterrence in the 21st Century'. Speech made at Chatham House Conference The UK and the World, 13 July 2010.

5 MoD. The Future of the United Kingdom's Nuclear Deterrent. Op. cit., pp.24-25.

6 Ibid., p.25, para. 5-4.

7 See, for example: Fox, op. cit.; Nick Harvey MP, Minister of State for the Armed Forces. Keynote address at RUSI Future Maritime Operations conference, 7 July 2010. Available on-line at .

8 See Allegra Stratton and Richard Norton-Taylor, 'Treasury and MoD Battle over Trident Replacement', The Guardian, 18 July 2010. Available on line at: <>. Accessed 23 July 2010.

9 There currently is a public debate taking place between Dr Fox and the Treasury as to whether the procurement costs for the renewal programme should be paid for from central funds or from the defence budget, uplifted or otherwise (see ibid., accessed 23 July 2010).

10 It would not be possible, for obvious reasons, to have a default setting within the missile whereby, at a given moment of sufficient divergence from its planned course, it would ascend or descend and detonate.

11 There are other submarine-basing and weapons load-out options which could be debated, for example developing a common class of submarine (a hybrid of an SSN and an SSBN) which could carry a variety of different weapons and thus offer greater flexibility in weapons load-outs. However, options such as this would have implications for the UK's strategic deterrent posture.


Lee Willett

Associate Fellow

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