(CNN) -- The U.S. Air Force's nuclear command has been rocked by a cheating scandal involving nearly three dozen officers.
Cheating on a proficiency exam involving intercontinental missile launch officers at the Global Strike Command at Malmstrom Air Force base in Montana apparently was carried out around last August and September by text and appears to be the largest incident of its kind, the Pentagon said.
"This is absolutely unacceptable behavior and it is completely contrary to our core values in the Air Force and as everybody here knows, the No. 1 core value for us is integrity," Air Force Secretary Deborah Lee James told reporters.
Officials said the nuclear arsenal is secure.
The case involving 34 officers with the 341st Missile Wing stemmed from a drug possession investigation at multiple air bases in the United States and overseas. Two of those caught up in the cheating episode have been linked to the other probe, officials said.
Sixteen officers were ultimately found to have actually cheated on the monthly proficiency exam while the rest knew the answers had been shared with others and did not report the violation, the Pentagon said.
All those disciplined in the investigation are no longer certified to conduct nuclear operations. Air Force Chief of Staff Gen. Mark Welsh indicated there are enough officers on hand to securely maintain the nuclear missiles in Montana.
He also echoed concern expressed by James about the integrity of the officers overseeing those caught up in the widespread cheating.
"We're going to look into this with every means at our disposal," he said.
Defense Secretary Chuck Hagel "was deeply troubled" to learn of the allegations and "he strongly supports the aggressive steps the Air Force is taking in response to them," Pentagon spokesman Rear Adm. John Kirby said in a statement.
Hagel just returned from visiting ICBM officers in Wyoming.
There are approximately 190 officers overseeing readiness of nuclear weapons systems in Montana, meaning the scandal has touched nearly 20% of that force.
The Air Force said all officers in the command will be re-tested by the end of Thursday.
This is the latest incident to rock the Air Force nuclear operations.
Last year, a missile unit at Malmstrom failed a safety and security inspection.
They operate about a third of the 450 Minuteman III nuclear-tipped intercontinental ballistic missiles in the U.S. force, according to the Air Force statement.
Also last year, another outfit based at Minot, North Dakota, did poorly in an inspection, resulting in the removal of 17 military personnel from their jobs.