Defense Secretary Chuck Hagel demanded more information Wednesday after the Air Force removed 17 launch officers from duty at a nuclear missile base in North Dakota over what a commander called “rot” in the force. The Air Force struggled to explain, acknowledging concern about an “attitude problem” but telling Congress the weapons were secure.

Hagel reacted strongly after the unprecedented sidelining of the officers at Minot Air Force Base, N.D., where one of their commanders complained of “such rot” that even the willful violation of safety rules — including a possible compromise of launch codes — was tolerated.

An internal email written by Lt. Col. Jay Folds, deputy commander of the 91st Operations Group, which is responsible for all Minuteman 3 missile launch crews at Minot, lamented the remarkably poor reviews the crews received in a March inspection. Their missile launch skills were rated “marginal,” which the Air Force said was the equivalent of a “D” grade.

“We are, in fact, in a crisis right now,” Folds wrote in the email to his subordinates.

In response, the Air Force said the problem does not suggest a lack of proper control over the nuclear missiles but rather was a symptom of turmoil in the ranks.

“The idea that we have people not performing to the standard we expect will never be good and we won’t tolerate it,” Gen. Mark Welsh, the service’s top general, said when questioned about the problem at a congressional hearing on budget issues.

Welsh’s civilian boss, Air Force Secretary Michael Donley, suggested the fact that Minot commanders identified 17 underperformers was evidence that the Air Force has strengthened its monitoring of the nuclear force. He stressed that launch crew members typically are relatively junior officers — lieutenants and captains — with limited service experience.

It is the duty of commanders, Donley said, to “ride herd” on those young officers with “this awesome responsibility” of controlling missiles capable of destroying entire countries.

Donley noted that he is particularly sensitive to any indication of weakness in the nuclear force because he took over as Air Force secretary in October 2008 after his predecessor, Michael Wynne, was fired by then-Defense Secretary Robert Gates for a series of nuclear embarrassments. Donley was charged with cleaning up the problem.

The Air Force said Wednesday that the two other missile wings — at Malmstrom Air Force Base, Mont., and at F.E. Warren Air Force Base, Wyo. — earned scores of “excellent” in the most recent inspection of their ICBM launch skills. That is two notches above the “marginal” rating at Minot and one notch below the highest rating of “outstanding.” Each of the three wings operates 150 Minuteman 3 missiles.

Sen. Dick Durbin, D-Ill., chairman of the Senate Appropriations defense subcommittee, expressed outrage, telling Welsh and Donley that the problem “could not be more troubling.”

The tip-off to trouble was the March inspection that earned the equivalent of a “D” grade when the unit was tested on its mastery of Minuteman 3 missile launch operations. In other areas, the officers tested much better, but the group’s overall fitness was deemed so tenuous that senior officers at Minot decided, after probing further, on an immediate crackdown.

In April the Air Force quietly removed the 17 officers.

The 17 cases mark the Air Force’s most extensive sidelining ever of launch crew members, according to Lt. Col. Angie Blair, a spokeswoman for Air Force Global Strike Command, which oversees the missile units as well as nuclear-capable bombers.

In his congressional testimony, Welsh said Folds and other senior commanders determined that the problematic launch officers had “more of an attitude problem than a proficiency problem.”

Advising his troops on April 12 that they had “fallen,” Folds wrote that drastic corrective action was required because “we didn’t wake up” after the March inspection that he said amounted to a failure, even though the unit’s overall performance technically was rated “satisfactory.”