The Air Force has put problems with misbehavior among nuclear launch officers behind it but won't lower its vigilance and will keep implementing cultural change within the ranks, the new commander of the nation's land-based nuclear missiles said Monday.

Maj. Gen. Anthony J. Cotton formally took command of the 20th Air Force, which includes intercontinental ballistic missile wings based at F.E. Warren Air Force Base in Cheyenne, Minot Air Force Base near Minot, North Dakota, and Malmstrom Air Force Base in Great Falls, Montana.

The wings oversee 450 Minuteman 3 nuclear missiles.

Problems at Malmstrom in recent years have included drug use and cheating on tests. The wider land-based ICBM force also has suffered in recent years from low morale, disciplinary problems, lack of resources, training lapses and leadership failures.

Changes to address those problems began more than two years ago, Cotton said following the change-in-command ceremony inside a cavernous maintenance building at F.E. Warren.

"I think each and every one of us understand that when we talk about changes in culture, it's not something that can happen in 25 months," Cotton said. "We will continue to push for that culture change."

Cotton, who is black, will be the first minority commander of the 20th Air Force. He previously was deputy director of the National Reconnaissance Office.

Present for the ceremony were Gen. Robin Rand, commander of the Air Force Global Strike Command and the first four-star general in charge of the nation's entire nuclear force since the Cold War era, and Adm. Cecil D. Haney, commander of the U.S. Strategic Command.

Updating the aging electronics of the Minuteman 3 will be among the top challenges facing the 20th Air Force in the years ahead, Haney said after the ceremony.

"The good news is, those designers that built it, built it to last. But we will have to replace it," Haney said.

The previous 20th Air Force commander, Maj. Gen. Jack Weinstein, was promoted to lieutenant general. He will return to the Washington, D.C., area as assistant Air Force chief of staff for strategic deterrence and nuclear integrations.