Six leaders — including two commanders and four of their subordinates — were fired from a key Air Force nuclear base in North Dakota without explanation Monday. Mayer’s group supports daily operations of the base’s 28 B-52H Stratofortress nuclear-capable bombers, 165 Minuteman III nuclear-tipped intercontinental ballistic missiles and launch control centers, and eight UH-1N helicopters, according to an official biography that was removed from Minot’s website Monday. Firings have come in response to widespread cheating on the monthly proficiency test for missileers, mishandling of nuclear weapons, unprofessional conduct and drug use