Theresa May is set today to become Britain's second Prime Minister.
On her first day, though, after being shown her new office and shaking hands with all the officials, she has the sober task of writing "the letter of last resort."
This note instructs commanders of the Trident missile submarine patrol in case of a devastating nuclear attack against the United Kingdom.
Before she writes the letter, she will be briefed by Chief of Defense Staff Sir Nicholas Houghton, who will explain the damage a Trident missile could cause.
She will then be left alone to handwrite four identical letters. Unless they are ever used, only the Prime Minister knows what they contain.
The letters will be kept inside two safes in the control room of each of the four submarines.
After a PM leaves office, the letters are destroyed.