WASHINGTON (AP) — Air Force officials tell The Associated Press that twice this year, officers entrusted with the launch keys to nuclear-tipped missiles have been caught leaving open a blast door. That door is intended to help prevent a terrorist or other intruder from entering the officers' underground command post and potentially compromising secret launch codes.

Transgressions such as this are rarely revealed publicly. But officials say they have happened, undetected, many more times than in the cases of the four officers who were given administrative punishments this year.

The blast door violations are another sign of serious trouble in the handling of the nation's nuclear arsenal.

The crews who operate the missiles are trained to follow rules without fail because the costs of mistakes are so high.