Air Force officials say a culture of fear that made launch officers believe they had to get perfect test scores to be promoted fueled a widening cheating scandal within the military's nuclear missile corps.

Half of the 183 launch officers at Malmstrom Air Force Base in Montana have been implicated and suspended.

Air Force Secretary Deborah Lee James says the scandal hasn't affected the safety or reliability of the military's nuclear mission.

Speaking to Pentagon reporters Thursday, Air Force officials said that it appears the cheating was confined to the Montana base, though a climate of frustration, low morale and other failures permeates the nuclear force.

The cheating scandal is the latest in an array of troubles that now have the attention of senior defense officials.