WASHINGTON  - Thirty-four US Air Force nuclear weapons officers cheated on a proficiency test or knew cheating was going on and kept quiet, the Pentagon said Wednesday.

The offending officers, who were “decertified,” comprise nearly a fifth of the officers tasked with monitoring the Air Force’s nuclear arsenal, CNN reported. “This was a failure of integrity,” Air Force Secretary Deborah Lee James said.

Sixteen cheaters used text messages to share exam answers, officials said while the rest of the officers knew the cheating was taking place and failed to report it, CNN said.

“This is absolutely unacceptable behaviour and it is completely contrary to our core values in the Air Force,” said James, noting that the cheating as potentially the largest such incident in the Air Force’s history.

The 34 officers, ranging in rank from second lieutenants to captains, have been restricted from missile crew duty and have had their security clearances suspended while the investigation continues.

There are 600 launch officers responsible for operating the Air Force’s fleet of 450 Minuteman III intercontinental ballistic missiles (ICBMs). Three bases are responsible for 150 of the missiles each, they are: Malmstrom AFB, in Montana; Minot AFB in North Dakota; and F.E. Warren AFB in Wyoming.

The launch officers spend 24 hours shifts in underground launch centres where they are responsible for ICBM missiles based in missile silos in the surrounding countryside.