From 2020: > During the time following a perceived attack, a series of progressive checks are made by submarine crews leading up to the captain opening the let

From 2020: > During the time following a perceived attack, a series of progressive checks are made by submarine crews leading up to the captain opening the letter. These include trying to listen for radio transmissions from various levels of Royal Navy and Ministry of Defense command using multiple methods, and most famous of all, listening for new radio broadcasts by BBC Radio channel four, and specifically new episodes of BBC Today. […] * https://www.twz.com/7300/letters-of-last-resort-are-post-apocalyptic-orders-for-uk-vanguard-sub-crews https://www.twz.com/7300/letters-of-last-resort-are-post-apo... Also: * https://en.wikipedia.org/wiki/Letters_of_last_resort https://en.wikipedia.org/wiki/Letters_of_last_resort