At the height of the cold war, US nuclear weapons were protected by an eight-figure password which was supposed to be difficult to crack.
In 1962 JFK signed the National Security Action Memorandum 160 which ordered nukes to have a Permissive Action Link (PAL) installed. This was a small device that ensured that the missile could only be launched with the right code and with the right authority.
But according to todayifoundout the US military put such an emphasis on a rapid response to an attack on American soil, that to minimise any delay in launching a nuclear missile, it set the launch codes at every silo in the US to 8 zeroes.
This solved the problem that some of the US nukes were stored in silos which had an unstable leadership. The US was worried that the nukes could be seized by those governments and launched. Kennedy reasoned that PAL would stop this sort of thing because they might get the warhead but they could not crack the code.
However, the military was worried that if the Russians did launch a strike, then its personnel would be running around trying to remember the number.
Even with the daft password, the US military dragged its feet on PAL, and it took 20 years before all US nukes had the technology.
Robert McNamara, JFK's Secretary of Defence personally tried to install tricky codes in the machine, but the Strategic Air Command hated him so much that almost as soon as he left, the code to launch the missiles was set to 00000000.
Firing crews were actually told to double-check the locking panel in underground launch bunkers to ensure that no digits other than zero had been inadvertently dialled into the panel.
This means that all those movies where everyone is waiting for the President to give his order to launch were pure fantasy. If the Russians had launched a strike, then the US would respond long before the President knew about it.