Letters of last resort



The letters of last resort are four identically-worded handwritten 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 official act of Her Majesty's Government.

The letters are stored inside two safes in the control room of each submarine. The letters are destroyed unopened after a Prime Minister leaves office, so what action would have been taken is only ever known to the outgoing Prime Minister.

Process
In the event of the death of the Prime Minister and the designated alternative decision-maker as a result of a nuclear strike, the commander(s) of the nuclear submarine(s) (at any time at least one is on patrol) will use a series of checks to ascertain whether the letters of last resort will have to be opened.

According to Peter Hennessy's book The Secret State: Whitehall and the Cold War, 1945 to 1970, the process by which a Trident submarine commander would determine if the British government continues to function includes, amongst other checks, establishing whether BBC Radio 4 continues broadcasting. In 1983, the procedure for Polaris submarines was to open the envelopes if there was an evident nuclear attack, or that all UK naval broadcasts had ceased for four hours.

Options
According to the December 2008 BBC Radio 4 documentary The Human Button, there were four known options given to the Prime Minister to include in the letters. The Prime Minister instructs the submarine commander to:
 * retaliate with nuclear weapons;
 * not retaliate with nuclear weapons;
 * use his/her own judgement; or
 * place the submarine under allied country command - if possible.

Fiction
David Grieg's 2012 play The Letter of Last Resort deals with the consequences and paradoxes of the letters. It was dramatised for BBC Radio 4, directed by Nicolas Kent and first broadcast on 1 June 2013.

A similar process was used in the book Down to a Sunless Sea, in which the planes of Air Britain, the country's only remaining civilian airline, were instructed on what to do in the event that the UK was struck by nuclear weapons. The instructions were in the form of a special letter in a sealed compartment in the cockpit. The special instructions were to be used if the company dispatcher issued an "Armada Signal" or if the plane was unable to return to the UK because its airports had been destroyed by nuclear strikes.