https://sgs.princeton.edu/00000000
https://arstechnica.com/tech-policy/2013/12/launch-code-for-...
https://en.m.wikipedia.org/wiki/Permissive_action_link
> According to nuclear safety expert Bruce G. Blair, the US Air Force's Strategic Air Command worried that in times of need the codes for the Minuteman ICBM force would not be available, so it decided to set the codes to 00000000 in all missile launch control centers. Blair said the missile launch checklists included an item confirming this combination until 1977.[7] A 2014 article in Foreign Policy said that the US Air Force told the United States House Committee on Armed Services that "A code consisting of eight zeroes has never been used to enable a MM ICBM, as claimed by Dr. Bruce Blair."[8] The Air Force's statement (that 00000000 was never used to enable an ICBM, i.e. the weapons were not actually launched) does not contradict Blair's statement (that 00000000 was the code for doing so).