America's gaggle of "Minuteman" long-range nuclear missiles went on line for the first time during the Cuban missile crisis in 1960 1962. But the world was supposedly protected from mutual assured destruction by the "Permissive Action Links" (PALs) which required an 8-digit combination in order to launch. Robert McNamara, then the U.S. Secretary of Defense, personally oversaw the installation of these special locks to prevent any unauthorized nuclear missile launches. He considered the safeguards to be essential for strict central control and for preventing nuclear disaster.
But what Secretary McNamara didn't know is that from the very beginning, the Strategic Air Command (SAC) in Omaha had decided that these locks might interfere with any wartime launch orders; so in order to circumvent this safeguard, they pre-set the launch code on all Minuteman silos to the same eight digits: 00000000.
For seventeen years, during the height of the nuclear crises of the Cold War, the code remained all zeros, and was even printed in each silo's launch checklist for all to see. The codes remained this way up until 1977, when the service was pressed into activating the McNamara locks with real launch codes in place. Before that time, the the lack of safeguards would have made it relatively easy for a small group of rogue silo officers or visitors to implement an unauthorized nuclear missile launch.
From the Center for Defense Information article:
Technically, crew members can launch a nuclear attack with or without approval from higher authority. Unless PAL or its equivalent forecloses this option, as many as 50 missiles could be illicitly fired.
Military personnel, e.g. maintenance airmen, and civilian contractors who possessed minimal security credentials were granted LCC access, and annually thousands of visitors holding no clearance whatsoever were permitted access to operational LCCs. In the interest of public relations, the Air Force permitted ready access to the Minuteman launch network by practically anyone desiring it.
One must also recite the obvious point that silos and launch control centers are loated [sic] in desolate reaches of the heartland. Reaction times to mount a counterterror offensive pinpointed at one or a few of these facilities would be measured in hours, not minutes or seconds.
The men and women running SAC in 1960 essentially put the entire planet's population at risk by deliberately disabling the PAL safety mechanisms. Perhaps we should keep that in mind before we put too much trust in the people charged with our nation's defense.
Note: The facts cited in this article have been disputed, though they are in agreement with the information from the Center for Defense Information. But skepticism is a healthy thing, and grains of salt are always go well with information obtained online.