The Air Force's top leaders explained to Congress Wednesday why commanders removed 17 officers from overseeing the service's most powerful nuclear missiles.

Lawmakers on May 8 questioned Air Force Secretary Michael Donley and Air Force Chief of Staff Gen. Mark Welsh about the incident, in which 17 officers with the 91st Missile Wing at Minot Air Force Base, N.D., were temporarily stripped of their authority to launch Minuteman III intercontinental ballistic missiles due to inspection failings.

"I don't believe we have a nuclear surety risk at Minot Air Force Base," Welsh said during a Senate Appropriations defense subcommittee hearing. "I believe we have commanders who are taking very aggressive action to make sure that never occurs, and in that respect, this is a good thing."

The Associated Press first reported the "unprecedented" sidelining of the launch officers, which occurred following an inspection in March.

The inspection shortcomings are the latest setbacks for the service’s nuclear force. In 2007, a B-52 bomber was mistakenly loaded with six nuclear warheads and flew from Minot Air Force Base to Barksdale Air Force Base, La., triggering a widespread investigation and reorganization within the service.

Sen. Dick Durbin, D-Ill., chairman of the subcommittee, said the newest incident “could not be more troubling," given the recent history.

“Can you explain to me how we could possibly reach the point with this critical assignment within the U.S. Air Force where there would be such a lack of professionalism and readiness at this high level?" Durbin asked.

Donley, who came into office in 2008 after his predecessor was fired following the the B-52 incident, said the Air Force over the past several years has "significantly" strengthened its process for inspecting missile units.

“I am confident in the Air Force’s ability to maintain a safe and secure nuclear deterrent,” he said.

The officers involved were mostly lieutenants and some may have been new to the service, Donley said. They received satisfactory ratings in other areas of the inspection, but needed retraining so the commander “took them offline to do that,” he said. “That is an appropriate command response.”

Durbin questioned whether there was a breakdown of supervision. “It is cold comfort to hear these are lieutenants and they may have been new to the job,” he said. “When I consider this responsibility -- that is as troubling as the disclosures that we’ve found.”

Welsh later said the unit passed the overall inspection with a rating of excellent or satisfactory in 21 out of 22 areas. It received a marginal rating in just one category: crew operations, which raised a red flag, he said.

“There was more of an attitude problem than a proficiency problem,” Welsh said. “I believe this is the kind of commander intervention that prevents the incidents that occurred in 2007. They took very aggressive action early to make sure that there was no question in the minds of their crew force that marginal behavior or sort of satisfactory just above the line was not acceptable."

One of the commanders, Lt. Col. Jay Folds, in an internal e-mail that was the basis for the Associated Press report, wrote of "rot" within the unit.

Welsh addressed this description specifically.

"I liked the way they responded. I wished they'd use different language in the e-mail they sent. The word 'rot' didn't excite me but it got my attention," Welsh told Congress.

The Air Force's public affairs office at the Pentagon later released a statement about the incident, saying the e-mail was an internal message "to the unit's officer crew force to re-emphasize the high standards expected in the nuclear mission area."

The statement also echoed comments made by Welsh during the hearing.

"Internal assessments and higher headquarter inspections help identify issues before they become serious problems,” it stated.