Actually the British version is less unsettling, it's resting the command on four Captains of the Royal Navy. First they have to confirm that the UK has been destroyed (this means no government or no established military chain of command) then they have to establish the prime minister has been killed. After this they execute their last order, which is whatever is held on the letter, which could potentially be anything. It would likely be targets, but it could equally be orders to contact an ally for appropriate targets prior to launching a blind attack.