 Any B61 which has had the command disable facility used must be returned to Pantex for repair.The B61 can be set for airburst, parachute retarded airburst, ground burst, parachute retarded ground burst, or laydown detonation, and can be released at speeds up to Mach 2 and altitudes as low as .In the weapon's laydown mode, it detonates 31 seconds after weapon release.