Mole hole

A mole hole, officially designated the Readiness Crew Building (RCB), is a type of structure built by the United States Air Force at former Strategic Air Command (SAC) bases around the country during the 1950s and 1960s. RCBs were located adjacent to an Alert Ramp, also called a "Christmas Tree", where Ready Alert aircraft were parked. These aircraft were initially B-47 Stratojet aircraft armed with nuclear weapons, augmented by KC-97 Stratofreighter aerial refueling aircraft. As SAC introduced newer bomber and aerial tanker aircraft into its inventory, the B-47 and KC-97 were later superseded by B-52 Stratofortress, B-58 Hustler, FB-111 or B-1 Lancer bombers, augmented by KC-135 Stratotanker or KC-10 Extender aerial refueling aircraft.