After assuming office, a British prime minister must handwrite “letters of last resort,” which are given to each of the captains of U.K.’s nuclear submarine fleet. The letters contain instructions on what to do if radio contact is lost (presumably due to nuclear war wiping out the government): retaliate, don’t retaliate, or join forces with an ally. Once a new prime minister issues the letters of last resort, the old ones are destroyed without their content being publicly disclosed.