The US Air Force has suspended 34 officers entrusted with the American nuclear arsenal for allegedly cheating - or tolerating cheating by others - in routine proficiency tests.
The cheating scandal is the latest in a series of troubles to hit the air force.
They include deliberate violations of safety rules, failed inspections, breakdowns in training and evidence that the men and women who operate the missiles from underground command posts are suffering burnout.
In October, the head of the nuclear missile force was sacked for embarrassing behaviour, including drunkenness, while leading a US delegation to a nuclear exercise in Russia.
A "profoundly disappointed" Air Force Secretary Deborah Lee James, the service's top civilian official, said the alleged cheating at Malmstrom Air Force Base, Montana, was discovered during a previously announced probe of drug possession by 11 officers at several air force bases.
Two of the officers are also in the nuclear force and are suspected of participating in the cheating ring.
"This is absolutely unacceptable behaviour," James said of the cheating.
General Mark Welsh, the air force chief of staff, said it could be the biggest such scandal in the history of the missile force. Welsh said one launch officer at Malmstrom was found to have sent one or more text messages to 16 other launch officers with answers to their test.
Further questioning at Malmstrom determined that 17 other launch officers "self-admitted to at least being aware of material that had been shared".
He added: "We don't yet know how or if each of those officers used that material, but we do know that none of them reported the incident to their leadership."
There are about 190 intercontinental ballistic missile (ICBM) launch officers stationed at Malmstrom.
A spokesman for Defence Secretary Chuck Hagel said the Pentagon chief, who last week visited a nuclear missile base and praised the force for its professionalism, was "deeply troubled" to learn of the allegations.
The spokesman, Navy Rear Admiral John Kirby, said Hagel insisted he be kept informed of the inquiry's progress.
James said she would visit each of the air force's three nuclear missile bases next week to meet senior officers and learn more about conditions within the launch force.
She suggested the cheating was confined to the single case involving 34 officers.
But numerous missile officers have revealed confidentially that some feel compelled to cut corners on their monthly proficiency tests due to the intense pressure to score at the highest levels to advance in the force.
"I want all of you to know that, based on everything I know today, I have great confidence in the security and the effectiveness of our ICBM force," she said.
"And, very importantly, I want you to know that this was a failure of some of our airmen. It was not a failure of the nuclear mission."
James, who has been in the job only four weeks, said the entire ICBM launch officer force of about 600 was being retested this week.
Welsh said he knew of no bigger ICBM cheating scandal or launch officer decertification in the history of the missile force, which began operating in 1959.
Last spring, the air force decertified 17 launch officers at Minot Air Force Base, North Dakota, for poor performance and bad attitude.
The Air Force said at the time it was the largest-ever one-time sidelining of launch officers.
The drug probe that led to the discovery of alleged cheating was disclosed by the Pentagon last week. It said then that it involved officers at six bases - five in the US and one in Britain.