When you stop to reflect on it, given the imperfection of the human race it is remarkable that we haven't destroyed ourselves or the planet...yet. Our incredible luck when it comes to nuclear weapons stands out as a case in point.
Ran across an interesting article this weekend talking about the permissive action links (PALs) on American intercontinental ballistic missiles (in particular the minutemen) in the 1970s. These devices were supposed to ensure that nuclear weapons could not be accidentally launched or launched without proper authorization. The idea was the apart from the two keys which had to be turned in the launch control center a code had to be programmed into the system. This code would be sent only when an attack had been authorized.
Great theory and plan, very poor implementation. In the 1970s the Strategic Air Command decided that all of the minutemen codes should be set to 000000. That's right, effectively eliminating any need for a password and allowing any two launch men to release a minimum of fifty ICBMs before anyone could say boo. The SAC justification was that in a first strike by the Russians the codes wouldn't have time to be transmitted and we would lose our ability to blow up their half of the world. Seems we have had a launch on warning policy in reality for most of the time of the bomb. Article Reprint from the late 70s has more details.