The Mk-7, initially produced in 1952, was the first nuclear weapon that could be carried by USAF (and U.S. Navy) fighter aircraft. Although it was carried externally by fighters (F-84, F-100 and F-101), it also could be carried internally by bombers such as the B-57. Because of the lack of ground clearance when hung under a fighter, the Mk-7 had a lower fin that was stowed in a retracted position on the ground and was extended once the carrier fighter was in the air. Capable of either an air or ground detonation, the Mk-7 had a yield in the kiloton range. It became obsolete in 1968 and is no longer in service.