Hoping to boost sagging morale, U.S. Defense Secretary Chuck Hagel made a rare visit Thursday to an air force nuclear missile base and the men and women who operate and safeguard the nation's Minuteman 3 missiles. But his attempt to cheer the troops was tempered by news that launch officers at another base had been implicated in an illegal-narcotics investigation.

Two officers at Malmstrom Air Force Base in Montana are being investigated for allegations of drug possession, said a service spokesman in Washington, Lt. Col. Brett Ashworth. Both of those being investigated are ICBM launch officers with responsibility for operating intercontinental ballistic missiles.

The launch officers' access to classified information has been suspended, and they have been prohibited from serving on missile launch control duty while the air force is investigating, another defence official said. That official provided no further details and spoke only on condition of anonymity because he wasn't authorized to discuss the matter publicly by name.

At the Wyoming nuclear missile base, meanwhile, Hagel addressed officers and airmen after a series of security lapses and discipline problems that were revealed in Associated Press news stories in 2013. Officials have said the service members are increasingly tired of working in what can seem like oblivion. They win no battles, earn no combat pay and only rarely are given public credit of any kind.

Hagel Nuclear Forces

U.S. Defense Secretary Chuck Hagel speaks with airmen of the 20th Air Force 90th Missile Wing during a trip to F.E. Warren Air Force Base on Jan. 9, 2014 in Cheyenne, Wyo. It was the first time since 1982 that a defence secretary has visited the nuclear missile base. (Blaine McCartney, Wyoming Tribune Eagle/Associated Press)

"You are doing something of great importance to the world," Hagel told the group. Lest they sometimes doubt that importance, he said, "You have chosen a profession where there is no room for error — none."

He made no direct reference to the problems revealed in the past year but declared, "How you do the job is really as important as the job itself. We depend on your professionalism."

A day earlier, he said he realized the ICBM workforce has morale issues.

"It is lonely work," he said. "They do feel unappreciated many times."

Higher rate of courts-martial

F.E. Warren Air Force Base, which is headquarters for the organization in charge of all 450 U.S. intercontinental ballistic missiles, has about 3,100 enlisted airmen and officers and saw 12 courts-martial in 2013, compared with nine the year before, 12 in 2011 and eight in 2010, according to air force statistics provided to the AP last week in response to a Freedom of Information Act request.

In each of the past four years, the courts-martial rate at F.E. Warren was higher than in the air force as a whole

The AP documented problems that go well beyond low morale in a series of stories in 2013, including one that disclosed that an ICBM operations officer had complained of "rot" infesting his missile force. Since then the service has tried to improve nuclear operations, but problems remain, including attitude issues, leadership lapses and, far more perilously, security lapses such as troops taking naps during 24-hour shifts with the blast door of their launch control center open. That could leave the missiles and airmen vulnerable and violates air force rules. A RAND Corp. study done for the Pentagon also found signs of burnout and behavioural problems such as domestic violence.