Letters of last resort

The United Kingdom relies on the use of four Vanguard-class submarines to provide its nuclear deterrent. The submarine can carry 16 Trident II SLBMs, a ballistic missile armed with nuclear warheads with a range of 7000 miles. The submarine does not have to refuel as she runs on a nuclear reactor and could theoretically remain underwater, circling the globe for approximately 20 years — only the need for supplies prevents this. At least one submarine is always active and armed, lurking beneath the world's oceans whilst the other three will either be in re-fit or in port.

The letters of last resort are four identically-worded, hand written letters written by the Prime Minister of the United Kingdom to the commanding officers of the four British ballistic missile submarines. They contain orders on what action to take in the event that an enemy nuclear strike has destroyed the British state and has killed or incapacitated the Prime Minister and the "second person" (normally a high ranking member of the Cabinet) whom the Prime Minister has designated to make a decision on how to act in the event of the Prime Minister's death. In the event that the orders were to be carried out, the action taken could be the last act of the British state, and has the capability of figuratively destroying the world.

The letters are stored inside two safes in the control room of each submarine. The letters are destroyed unopened whenever a Prime Minister leaves office, so what action to take is only ever known to the outgoing Prime Minister.^{[citation needed]}

Process

In the event of the death of the Prime Minister and the designated alternate decision-maker as a result of a nuclear strike, the commander(s) of the nuclear submarine(s) (of which there is always one still active) will use a series of checks to ascertain whether the letters of the last resort will have to be opened. According to Peter Hennessy's book Secret State: Whitehall and the cold war 1945 to 1970, the process by which a Trident submarine would determine if the British government continues to function includes, amongst other checks, establishing whether BBC Radio 4 continues broadcasting.

Options

Although the final orders of the Prime Minister are at his or her discretion and no fixed options exist, four known options are often presented to Prime Ministers by military advisers when writing such letters of last resort:

1. Captain ordered to retaliate to the nuclear attack on the UK with the use of nuclear weapon(s). Retaliation would result in launching the submarine's nuclear weapon(s), most likely against the instigator(s) of the nuclear attack on the UK. Prime minister could also specify if retaliation should be a tit-for-tat response.
2. Captain ordered not to retaliate to the nuclear attack on the UK with use of nuclear weapons. The prime minister may well consider that the nuclear deterrent has failed and retaliation could result in mutual assured destruction and nuclear war. Consequently, such retaliation may be considered futile and unwise if the existence of humanity is at risk.
3. Captain given prerogative to act of his own accord and ordered to take decision based on his judgment. Prime Minister has refused or failed to give a clear order in the letter. Consequently, it is up to the captain to decide what action to take, such as to retaliate or back down.
4. Captain ordered to place himself and his submarine under the command of an allied nation. The Prime Minister could give responsibility of what action to take to the Prime Minister or President of the designated ally nation(s). One of these designated nations could be one of the monarch's Commonwealth realms such as the Government of Australia or Government of Canada depending on both the location of the given vessel and current geopolitical issues. Alternatively, the Prime Minister may well give command of what action to take to a fellow nuclear power such as the President of the United States or the President of the French Republic for example. In addition, the Prime Minister may ask the captain to relay commands to allied nations, state what level of authority they will have over the use of his submarine and whether to place the UK's nuclear arsenal under the command of an allied nation.

This system of issuing notes containing orders in the event of the head of government's death is said to be unique to the United Kingdom although the concept of written last orders, particularly of a ship's captain, is a naval tradition, with other nuclear powers using different procedures.

Past Prime Ministers

Only one former Prime Minister, James Callaghan, has publicly given any insight on his orders. Callaghan stated that, although in a situation where nuclear weapon use was required, and thus the whole purpose and value of the weapon as a deterrent had failed, he would have ordered use of nuclear weapons, if needed: If we had got to that point, where it was, I felt it was necessary to do it, then I would have done it (used the weapon). But if I had lived after pressing that button, I could have never forgiven myself.

See also

• Dead Hand (nuclear war)
• Mutually assured destruction
• Nuclear deterrent

External links

• HMS Apocalypse: Deep Atlantic submarine waits alert for nuclear missiles to end the World, London: The Daily Mail, 30 November 2008, http://www.dailymail.co.uk/news/article-1090400/HMS-Apocalypse-Deep-Atlantic-submarine-waits-alert-nuclear-missiles-end-world--.html .
• "The Human Button", Radio 4, BBC, http://www.bbc.co.uk/radio4/factual/pip/fseue/ .
• Rosenbaum, Ron, "The Letter of Last Resort", Slate Magazine (article), http://www.slate.com/id/2208219/pagenum/all 
• "Prologue" (radio archive), This American Life, http://www.thisamericanlife.org/radio-archives/episode/399/Contents-Unknown?bypass=true .