PALs evolved from the need to exert greater negative control over nuclear weapons. Contrary to popular belief, the original motivation was not to guard against unauthorized actions by rogue American military officers. To be sure, this was not a negligible threat. More than one Strategic Air Command head was interested in starting World War III; one was later described this way by another general who reported to him:
I used to worry about General Power. I used to worry that General Power was not stable. I used to worry about the fact that he had control over so many weapons and weapon systems and could, under certain conditions, launch the force. Back in the days before we had real positive control [i.e., PAL locks], SAC had the power to do a lot of things, and it was in his hands, and he knew it.
A more pressing concern was foreign access. Under the auspices of NATO, assorted nuclear weapons were at least partially controlled by other nations. This was worrisome, especially to Congress, and in violation of U.S. law. Worse yet, some of our allies were seen as potentially unstable; there was considerable fear that the military in one of these countries might override even their own civilian leadership. Stein and Feaver cite France as one possible example, and possibly Germany and Turkey:
The exact details are hazy, but the broad contours are clear: the inspection team found the control of the forward-based nuclear weapons inadequate and possibly illegal. In Germany and Turkey they viewed scenes that were particularly distressing. On the runway stood a German (or Turkish) quick-reaction alert airplane (QRA) loaded with nuclear weapons and with a foreign pilot in the cockpit. The QRA airplane was ready to take off at the earliest warning, and the nuclear weapons were fully operational. The only evidence of U.S. control was a lonely 18-year-old sentry armed with a carbine and standing on the tarmac. When the sentry at the German airfield was asked how he intended to maintain control of the nuclear weapons should the pilot suddenly decide to scramble (either through personal caprice or through an order from the German command circumventing U.S. command), the sentry replied that he would shoot the pilot; Agnew directed him to shoot the bomb.
After this incident, Harold Agnew came up with the idea of the PAL. In a discussion of the French need for PALs on their own weapons, Stein and Feaver say this:
France's history has not been characterized by the same orderliness of political succession and civil-military relations as Great Britain's. Indeed, there have even been moments of instability in the nuclear age. During the revolt of the generals against De Gaulle in 1960, for example, the government ordered the detonation of a nuclear device in Algeria so that it would not fall into the hands of the military.