The US Air Force has stripped an unprecedented 17 officers of their authority to oversee nuclear missiles, after a string of failings that the group's deputy commander said stemmed from "rot" within the ranks. The suspensions followed a March inspection of the 91st Missile Wing at Minot Air Force Base, North Dakota, that resulted in a "D" grade for the team tested on its mastery of the Minuteman III missile launch operations system.

"We are, in fact, in a crisis right now," the group's commander, Lieutenant Colonel Jay Folds, wrote in an internal email that was obtained by the Associated Press and confirmed by the Air Force. The Air Force had publicly described the inspection as a success.

The news follows a series of incidents in recent years that have uncovered major problems with the oversight of the US's nuclear arsenal. In 2007, airmen at Minot accidentally loaded a B-52 with six nuclear weapons. The aircraft then flew to Barksdale Air Force Base, Louisiana. In another incident, nuclear weapons parts were mistakenly shipped to Taiwan. The defense department learned of the error in 2008, 18 months after the fuses for nuclear warheads were shipped.

Minot's crew are supposed to stand ready 24-hours a day to launch missiles on the president's command. A crew member was disciplined in 2008 for falling asleep on duty, while watching nuclear launch-code components.

The 17 officers were part of a team standing 24-hour watch over the Air Force's most powerful nuclear missiles, intercontinental ballistic missiles (ICBMs) that can strike targets across the globe. They were removed from duty in April. "You will be a bench warmer for at least 60 days," Folds wrote.

The suspensions are believed to be the most extensive ever. According to the email obtained by AP, Folds moved to discipline the crew after "such rot in the crew force" that a pattern of weapons safety rule violations, possible code compromises and other failings had arisen "all in the name of not inconveniencing yourselves", Folds wrote.

Folds said the crew had also questioned their superiors' orders and failed to show proper respect. An earlier inspection had been deemed "satisfactory" but problems had worsened, he said. "We are breaking you down, and we will build from the ground up," Folds wrote. In another message, he wrote: "It takes real leaders to lead through a crisis and we are, in fact, in a crisis right now."

Minot's latest crisis follows a 2008 Pentagon report that found a "dramatic and unacceptable decline" in the Air Force's commitment to the mission, which has its origins in a Cold War standoff with the Soviet Union. Ahead of the report the then defense secretary, Robert Gates, sacked the Air Force secretary and chief of staff. The Air Force has since taken numerous steps to improve its nuclear performance.

The Air Force told AP that the latest lapses had not put the security of the nuclear force at risk. It said the officers who lost their certification to operate ICBMs were now getting more training, with the expectation that they will return to normal duty within about two months. The missiles remained on their normal war footing, officials said.

Bruce Blair, who served as an Air Force ICBM launch control officer in the 1970s and is now a research scholar at Princeton University, said the Folds email pointed to a broader problem within the nuclear weapons force.

He said problems were not confined to Minot and that the lack of discipline was "extremely worrying". Blair said the jobs were seen as "dead end" positions. "It's tedious work, you are out in the middle of nowhere and answer to nobody," he said. He said problems had been growing for decades and "raised serious concerns about the safety and security of the nuclear missile force".

Blair said the missile system had been set up for a full-scale war for Russia and that it was largely now obsolete. "The force has always been second fiddle to the flying force," he said. Morale had worsened after a decision earlier this year to end a scheme where the nuclear watch crews could train and transfer to more covetable positions in areas like space operations. "That really angered the crew force," he said.

Blair is co-founder of Global Zero, an international group that advocates the eventual elimination of nuclear weapons. In 2011, the defense secretary Chuck Hagel, who was then a senator, co-authored a report for Global Zero calling for a dramatic reduction in the US nuclear arsenal, of about 5,000 warheads and bombs, to about 900. "All these guys see the writing on the wall: the future is not nuclear," said Blair.

• This article was amended on May 8 2013. The picture was changed to reflect more accurately the content of the article.