Updated

The chairman of the Joint Chiefs of Staff on Monday was slated to visit a North Dakota Air Force base that has been plagued for years by missteps involving nuclear weapons.

Army Gen. Martin Dempsey's trip to Minot Air Force Base comes just days after the commander in charge of training and proficiency at the base's 91st Missile Wing was ousted due to "a loss of confidence." The base, which has suffered a rash of nuclear-related blunders for several years, scored an equivalent of a "D'' grade for its mastery of missile launch operations during a test in March.

The Air Force, however, downplayed Dempsey's planned stopover, saying the visit is intended as an opportunity to tour the base and meet with airmen and their families. Base spokeswoman Capt. Genieve David said Dempsey's tour has nothing to do with the base's history of nuclear-related embarrassments.

"The visit was preplanned," base spokesman Capt. Genieve David said. "It is ironic, but this visit had been planned for months."

The Minot base, home to about 4,800 active-duty military personnel, is one of the nation's two B-52 bomber bases and the command center for about 150 Minuteman III missiles, sunk in hardened silos across 8,500 square miles of northwest and north-central North Dakota.

The Air Force last week fired Lt. Col. Randy Olson, who headed the base's operations support squadron that conducts training, ensures crew proficiency and reinforces standards. The military said in a statement that it has lost confidence in Olson's "ability to provide necessary leadership."

The Associated Press reported last month that the Lt. Col. Jay Folds, the 91st Missile Wing's deputy commander of operations, complained to his officers in an internal Air Force email about "rot" within their ranks, including tolerance of weapons safety rules violations.

Nineteen launch crew members, representing about 10 percent of the force, were taken off duty for remedial training following a March inspection that rated the unit "marginal," when tested on launch skills. David, the base spokeswoman, said Monday that the military has reinstated 10 crew members.

The so-called missiliers spend 24-hour shifts underground in a 12-by-20 foot steel-and-concrete capsule, designed to withstand a nuclear attack. Each missile carries up to three warheads, capable of reaching a target 6,000 miles away in about 20 minutes should a presidential order come down. Missiles travel at 15,000 mph.

The bomber wing at the Minot base also has been under scrutiny for years, following a 2007 incident in which a B-52 bomber was mistakenly armed with six nuclear-tipped cruise missiles in Minot and flown to Barksdale Air Force Base in Louisiana.

The military called it an "unacceptable mistake."

Other lapses at the base followed the 2007 bomber flight, including two crashes of vehicles carrying missile parts in a little more than a year, the theft of a launch code device, the discovery of missile crew members sleeping on the job and failed inspections.

Then-Defense Secretary Robert Gates visited the base in 2008 and told airmen that lapses in nuclear weapons procedures were unacceptable and that "there is simply no room for error." The 2007 bomber flight was cited by Gates as one factor leading to the ouster of the Air Force's chief of staff and its secretary.

The Minot bomb wing commander at the time, Col. Joel Westa, assured Gates that "you'll be able to rest comfortably."

Westa was fired less than a year later, after the military said it lost confidence in his ability to command the base.