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Parliament is about to vote on renewing elements of our nuclear defence system, known as Trident. Some argue that we need it to keep the peace on the basis of Mutually Assured Destruction (MAD) - if both sides have nuclear missiles then neither would dare to use them. Others question the practicality, morality and cost of the nuclear option. Do we need it? Should we maintain it or scrap it? Should the UK keep its nuclear weapons?

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Research and writing: Paul Eustice; editing: Perry Walker. Content was reviewed by two people in the field with different perspectives: they preferred not to be named.

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What is Trident

Trident is our only nuclear defence system. Trident is strictly speaking the name of the missile involved. However, the submarines used to deliver the missiles are included in what we loosely call the Trident System. The current decision in relation to ‘Trident’ is not about new missiles but about renewing the submarines used to deliver Trident missiles (1).

Trident is based on the West Coast of Scotland. The submarines are at Faslane and the warheads are at Coulport, eight miles away.This location is important because the Scottish National Party does not want Trident on Scottish soil.

The ‘Trident’ system in more detail

It is not an ordinary battlefield weapon. It consists of:

  • Four submarines, each twice as long as a Jumbo Jet. One of them is always out on patrol.
  • 58 ballistic missiles (Trident)
  • In theory, each submarine could carry 16 Trident missiles and each missile could carry 12 independently-targetable nuclear warheads - 192 in all. Under a non-proliferation treaty we limit ourselves to a maximum of 40 warheads on each submarine when on patrol.

Each warhead has a yield of around 100 kilotons, which is around 8 times the power of the bomb that destroyed the city of Hiroshima. The total yield of all the warheads deployed on submarines based in Scotland is around 14.4 megatons, which is equivalent to over 1,000 Hiroshima bombs. (2)

Assuming we aimed at a ‘traditional’ enemy like Moscow, targeting underground command centres, and assuming we are so accurate we only hit what we aim at, 40 nuclear warheads could produce 5.4 million deaths, 4.5 million inside the city and a further 870,000 in Moscow Region. This is an estimate of casualties within the first few months and does not take account of long-term effects (3 p2)

There would be further complications from the effects on water supply, food chains, weather systems, lack of medical treatment etc. in the long term. The area would be uninhabitable for generations.

What is it for?

Put simply, the idea behind nuclear defence is ‘mutually assured destruction’, or MAD. If we own that sort of destructive power then nobody would dare to attack us. If both sides own it then, given the consequences of a nuclear exchange, they would be ‘mad’ to use it, so neither side would do so.

Expert views, including senior armed forces personnel, are split between the idea that it is irresponsible to scrap nuclear weapons and a conviction theyare now outmoded and actually harming our defence forces by using the funds we need for more conventional defence measures. (1, 5.2)

Why are we asking the question now?

“A debate and vote in the House of Commons on the general principle of whether the UK should retain a strategic nuclear deterrent beyond the life of the current system was held on 14 March 2007. That motion was passed … by 409 to 161 votes.”(4)

“In early 2016, a decision on taking that programme forward into the manufacture phase ... will be taken. The Government is expected to seek the approval of Parliament for this decision.” (1)

A recent newspaper report suggested the decision may even be brought forward to prevent the question of renewal becoming an element of any part of any Scottish election debate, due in May 2016. (5) There is a long lead-in time between approving and delivering any system. However, the new Leader of the Labour Party has already said that, if elected, he would never use it, raising fundamental questions aboutthelogic that underpins its existence. Would any Prime Minister actually use it? Does any potential enemy believe they would? Would we wish them to?

Is the question all about Trident?

In theory, we could elect to have various kinds of nuclear defence system , but a defence White Paper in 2006 concluded that:retaining a submarine-based system provides the most effective deterrent; and that no credible alternative is cheaper (6 p7)

The Trident Alternatives Review published in 2013 and the Trident Commission Concluding Report 2014 both concluded they could not recommend any other system as a practical replacement. (7, 8)

Is it a simple yes/no decision?

There is no alternative system in prospect. The Liberal Democrat suggestion of a cut-price, scaled down or part-time version of Trident - cheaper - a “minimal yet credible deterrent” - has not been widely supported in either of the Houses of Parliament (9, 10).

It is at present very unlikely the vote in parliament will include such any sort of alternative. Even if there were, the fundamental question is whether we should we own such a system in principle. Hence, on Open Up there are only two choices: Trident; or nothing.

Have any decisions been taken already?

The Chancellor, George Osborne, has already announced a £500 millionoverhaul for the Faslane naval base, where the Trident system is housed, to make sure it is ‘fit for purpose until at least 2067’ (11) However, Faslane is also used as a base for conventional submarines and opinions differ on whether he really intended to pre-empt the debate on renewing Trident.

What factors affect the decision?

The main criteria are laid out in the arguments on the next page. They can be grouped into three categories: practicality, morality and cost.

Not considered is the argument that renewing Trident would be illegal, because this argument seems unlikely to affect any vote. (7 p29)

Illegality, it has been argued, follows from our obligations under a range of treaties and agreements relating to nuclear weapons, especially Article VI of the Treaty on the Non-Proliferation on Nuclear Weapons (NPT). Under that article, the five recognised nuclear weapon states are permitted to possess nuclear weapons, but only if they commit themselves to the principles of nuclear arms control and eventual disarmament. However, “successive governments have insisted that the UK’s nuclear deterrent is fully consistent with all of the UK’s international legal obligations”. This is partly because we have been reducing our nuclear stockpile since the end of the Cold War (which ran roughly between the 1950s and the 1990s). By 2020 the UK will have reduced them by 65%, making it “the smallest of all the NPT nuclear weapon states”. It is said that this keeps us within the spirit of the law. (1; section 3)


1 Replacing the UK's Trident Nuclear Deterrent - briefing report in the House of Common Library number 7353, 26 October2015 - summary and full report at

2 Scottish CND

3 If Britain fired Trident - Scottish CND


7 Trident Alternatives StudyJuly 2013

8 Trident-commission-concluding-report

9 The Trident Successor Programme: An Update


11 Telegraph 17th November 2015

12 Diplomat

13 Kings College debate mp3

14The Myth of Nuclear Deterrence


16 Guardian article

17 Fight, fight and fight again - Progress - Luke Akehurst -31 October 2012


19 The Trident question - LRB - Christopher Prendergast 25 September 2015


21 Independentarticle by David ConnettSaturday 26 December 2015

22 Guardian article


24 BBC news 2015

25 Independent article Sean O'Grady 9th November 2015

26 National Security Strategy and Strategic Defence and Security Review 2015; May 2011 Parliamentary Report

27 Daily Mail

28 Mirror

29 Wings over Scotland

30 BBC 2008

31 Independent article

32 CND

33 Trident: the British Question Ian Jack Guardian Thursday 11 February 2016

34 Guardian article 34

35 "Progress Backing Trident renewal - Rowan Ree 5 November 2012

36 London Review of BooksVol. 33 No. 9 28 April 2011pages 32-33 R.W. Johnson

37 Independent article Sean O'Grady 9th Novem,ber 2015

38 Wings over Scotland

39 Labour’s Trident debate needs to be based on facts - John Hutton and George Robertson, Guardian, 22 February 2016