The U.S. Air Force says it has relieved six officers at a North Dakota nuclear missile base after their units failed a safety inspection. It’s not clear exactly what lapses prompted the firings. The Minot Air Force Base is home to more than two dozen B-52 nuclear-capable bombers, as well as 165 Minuteman III nuclear-tipped intercontinental ballistic missiles. This follows a previous safety lapse at the base in 2007, when a B-52 bomber flew to Louisiana carrying six nuclear-armed cruise missiles, without the knowledge of the flight’s crew.