The US Air Force has fired nine nuclear commanders and will discipline dozens of junior officers at a nuclear missile base after an exam cheating scandal.
A 10th commander, the senior officer at the base, resigned and will retire from the Air Force.
Air Force officials called the discipline unprecedented in the history of its Intercontinental Ballistic Missile (ICBM) force.
The moves come after a series of security and other problems in the force were revealed last year, including a failed safety and security inspection at Malmstrom Air Force Base, Montana, where the cheating occurred.
Colonel Robert Stanley, who commanded the 341st Missile Wing at Malmstrom, wrote a resignation letter in which he said the reputation of the ICBM mission was now "tarnished because of the extraordinarily selfish actions of officers entrusted with the most powerful weapon system ever devised by man".
Stanley, seen as a rising star in the Air Force, had been nominated for promotion to brigadier general days before the cheating scandal came to light in January.
Instead he is retiring, convinced, as he wrote in his farewell letter, that "we let down the American people on my watch".
Separately, another of the Air Force's nuclear missile units - the 90th Missile Wing at F.E. Warren Air Force Base, Wyoming - said it had fired the officer overseeing its missile squadrons. It said Colonel Donald Holloway, the operations group commander, was sacked "because of a loss of confidence in his ability to lead".
The 90th Missile Wing offered no further explanation for Holloway's removal and said it "has nothing to do" with the firings announced by the Air Force in Washington. Together, the moves reflect turmoil in a force that remains central to American defence strategy, but in some ways has been neglected. The force of 450 Minuteman 3 missiles is primed to unleash nuclear devastation on a moment's notice, capable of obliterating people and places halfway around the globe.
Air Force Secretary Deborah Lee James, the service's top civilian official, said a thorough review of how testing and training are conducted in the ICBM force has produced numerous avenues for improvements.
The cheating involved unauthorised passing of answers to exams designed to test missile launch officers' proficiency in handling "emergency war orders", which are messages involving the targeting and launching of missiles.
Nine key commanders below Stanley were fired, including the commanders of the 341st Wing's three missile squadrons, each of which is responsible for 50 Minuteman 3 nuclear missiles.
Members of all three missile squadrons were implicated in the cheating, either by providing or receiving test answers or knowing about the cheating and not reporting it.