One of Liz Truss’ first tasks will be to hand-write instructions to each of Britain’s four nuclear submarine commanders, instructing them how to react in the event of an all-out attack that would have killed her and destroyed the UK. They are known as letters of last resort. But first, Truss will receive a briefing from Britain’s military chiefs on how the Trident nuclear deterrent works – including the potential military and humanitarian consequences of authorizing a retaliation. The estimated 40 warheads available on a Vanguard submarine, which carries Trident missiles, have the ability to hit multiple cities and kill millions of people. “It’s called a deterrent for a reason,” a Navy source said. Tony Blair went “quite quietly”, according to Lord Guthrie, the chief of the defense staff who briefed him shortly after his 1997 election victory. John Major said it was “one of the hardest things I’ve ever had to do never”. Each warhead is believed to have an explosive yield of 100 kilotons, according to David Cullen of the Nuclear Intelligence Agency. That’s more than six times the 15-kiloton bomb dropped on Hiroshima at the end of World War II. It is not necessary for Truss to write the letters immediately after the notification. the new prime minister has time to think. The existing letters, written by Boris Johnson, can remain in place, apparently for the submarine currently at sea – at least one must be on patrol at all times for the nuclear deterrent to remain continuous. Most past prime ministers have not revealed what they wrote, although Jim Callaghan said: “If we had got to that point then I would have.” Although he added that if he had in fact survived after pressing the nuclear button, “I could never, never forgive myself.” Theresa May was asked, in a Commons debate on the renewal of Trident in 2016, whether she was willing to “authorise a nuclear strike that could kill 100,000 innocent men, women and children”. Yes, he replied, adding “the whole point of deterrence is that our enemies have to know we’re going to be ready to use it.” Once written, the letters are delivered, in a safe within a safe, to each of the four submarines. In fact, there are two letters for each submarine, the first of which contains instructions for the final steps to be taken before the safe can be opened with the second, from the prime minister. Archie Bland and Nimo Omer take you to the top stories and what they mean, free every weekday morning Privacy Notice: Newsletters may contain information about charities, online advertising and content sponsored by external parties. For more information, see our Privacy Policy. We use Google reCaptcha to protect our website and Google’s Privacy Policy and Terms of Service apply. A commander at sea has many ways of ascertaining whether the UK and its command and control systems are still in place by monitoring a wide range of communications, not just the Radio 4 transmission. There is also an established set of relievers and fall back mechanisms in the unlikely case of any doubt. 30 hours in office: Liz Truss’ journey to becoming PM – video timeline
