The Air Force announced Thursday that it has relieved nine mid-level commanders ­assigned to safeguard the nation’s nuclear arsenal following a ­wide-ranging probe into a test-

cheating scandal that implicated scores of airmen.

The dismissed officers, most of whom were colonels and lieutenant colonels, were not found to have facilitated or condoned the cheating at Malmstrom Air Force Base in Montana. But they were held accountable for creating a culture that enabled it, officials said.

The scandal, which came to light after a probe into suspected drug use among missileers at Malmstrom, has been among the most embarrassing ethical lapses the Pentagon has had to contend with in recent months. The military also faced questions about its ability to prosecute cases of sexual assault and is investigating a similar cheating scandal involving sailors.

“We do have some systemic issues in our missile community,” Air Force Secretary Deborah Lee James told reporters Thursday afternoon at the Pentagon. She called the cheating at Malmstrom a “major failure in integrity.”

Dozens of junior officers will face a range of disciplinary sanctions from letters of reprimand to court-martial, officials said.

In this image released by the U.S. Air Force, a Malmstrom Air Force Base missile maintenance team removes the upper section of an ICBM at a Montana missile site. (John Parie/U.S. Air Force via AP)

Investigators found that many airmen were sharing test questions and answers via text messages. In at least one case, officials said, classified material was exchanged in that manner.

Air Force officials said the cheating on job-proficiency tests became routine among airmen who described themselves as being demoralized. Many saw perfect scores as their only chance for promotion and career advancement.

“You’re competing for promotion against a pilot who can say he flew this many hours,” said Adam B. Lowther, a professor at the Air Force Research Institute who wrote a report on the scandal. “This leaves missileers with the perception that they are not fit for promotion.”

Lowther and senior officials said the cheating should not call into question the readiness of the team at Malmstrom, which oversees intercontinental ballistic missiles.

“While cheating was bad, cheating in the classroom was never going to put the actual weapons at risk,” Lowther said, arguing that problems at the base reflected an unreasonable drive for perfection rather than an ill-trained force.

“Crew members felt pressure to score 100 percent on each and every test,” Lt. Gen. Stephen Wilson, commander of the Air Force Global Strike Command, said Thursday. “They felt compelled to cheat to get a perfect score.”

Officials called the removal of the nine commanders from an Air Force wing unprecedented. Most are likely to be transferred to less-desirable staff jobs and are unlikely to be considered for promotion, because being removed from command generally does irreparable damage to a military career.

Col. Robert Stanley, commander of the 341st Missile Wing, the unit where the cheating took place, resigned from his position Thursday and will retire.

James said the Air Force intends to invest heavily in nuclear bases around the country in an effort to improve morale and working conditions. She also said the service will do more to instill the importance of integrity at every stage of an airman’s career.

Air Force officials said they had found no evidence that cheating on tests was pervasive at other nuclear bases.

“We talked to missile crews and talked to the instructors and leaders,” Lowther said. “What we couldn’t say was: There was cheating at Malmstrom so we will confiscate everyone’s cellphone. We can follow the evidence, but the evidence never said there was cheating anywhere else.”