The U.S. air force disclosed on Wednesday that 34 officers entrusted with the world's deadliest weapons have been removed from launch duty for allegedly cheating — or tolerating cheating by others — on routine proficiency tests. The announcement was a stunning setback for a nuclear missile force already beset by missteps and leadership lapses.

The cheating scandal is the latest in a series of air force nuclear stumbles documented in recent months by The Associated Press, including deliberate violations of safety rules, failures of 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 commander of the nuclear missile force was fired for engaging in embarrassing behaviour, including drunkenness, while leading a U.S. delegation to a nuclear exercise in Russia.

A "profoundly disappointed" Air Force Secretary Deborah Lee James, the service's top civilian official, told a hurriedly arranged Pentagon news conference that 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, including two who also are in the nuclear force and suspected of participating in the cheating ring.

"This is absolutely unacceptable behaviour," James said of the cheating, which Gen. Mark Welsh, the air force chief of staff, said could be the biggest such scandal in the history of the missile force.

A spokesman for Defence Secretary Chuck Hagel said the Pentagon chief, who just last week visited a nuclear missile base and praised the force for its professionalism, was "deeply troubled" to learn of the cheating allegations. The spokesman, navy Rear Adm. John Kirby, said Hagel insisted he be kept apprised of the investigation's progress.

Entire force to be retested

James said she will travel to each of the air force's three nuclear missile bases next week on a fact-finding mission to learn more about conditions within the missile launch force and the more senior officers who manage them. She suggested that the cheating was confined to this single case involving 34 officers, although numerous missile officers have told the AP confidentially that some feel compelled to cut corners on their monthly proficiency tests because of 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 is 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 a combination of poor performance and bad attitudes; at the time the air force said it was the largest-ever one-time sidelining of launch officers.

Test answers texted out

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, and that further questioning at Malmstrom determined that 17 other launch officers "self-admitted to at least being aware of material that had been shared. 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 ICBM launch officers stationed at Malmstrom.

The drug investigation that led to the discovery of alleged cheating was disclosed by the Pentagon last week. It said then that it involved 10 officers at six bases — five in the U.S. and one in England. On Wednesday, the air force said the number of suspects has grown to 11. Welsh said he could not comment further on the drug probe.