Thirty-four US Air Force officers in charge of launching nuclear missiles have been suspended over accusations that they cheated in proficiency tests.
The air force said some staff had texted answers to the routine tests to others, while others had known about the cheating but failed to report it.
The ranks involved range from 2nd lieutenants to captains.
The allegations emerged during investigations into alleged drug use by personnel at other bases.
Air Force Secretary Deborah Lee James said the cheating had involved officers based at the Malmstrom Air Force Base in Montana, and related to a monthly test all nuclear missile staff must take.
"Some officers did it," she said of the cheating. "Others apparently knew about it, and it appears that they did nothing, or at least not enough, to stop it or to report it."
Ms James said it was "absolutely unacceptable behaviour" but that the security of the nuclear programme was not in doubt.
"This was a failure of some of our airmen. It was not a failure of the nuclear mission," she said.
The 34 officers have had their security clearance revoked and the entire team in charge of overseeing missile launches will be re-tested.
A further three officers have been suspended for allegedly possessing recreational drugs.
It is the latest scandal to hit the air force and nuclear missile force.
In August, a nuclear missile unit at Malmstrom failed a safety and security inspection, leading to a senior security officer being relieved of duty.
And in May, it was reported that 17 officers in charge of maintaining nuclear missiles were sidelined over safety violations at Minot Air Force base in North Dakota.
In October, the general in charge of America's long-range nuclear missiles, Maj Gen Michael Carey, was sacked, with officials citing a "loss of trust and confidence".
It later emerged he had engaged in conduct "unbecoming of a gentleman" during a work trip to Russia in July.
Gen Carey's removal came days after the Navy sacked Vice-Adm Tim Giardina, second-in-command of the US Strategic Command, over illegal gambling.
Strategic Command oversees everything from America's land-based nuclear missiles to space operations governing military satellites.