Helicopter Mine Countermeasures Squadron 12 (HM-12) was the first of its kind. Established at NAS Norfolk, Virginia, on 1 April 1971, the Sea Dragons institutionalized airborne mine countermeasures (AMCM) as a role of U.S. Navy helicopters. HM-12 initially was equipped with CH-53A Sea Stallion helicopters—borrowed from the Marine Corps—capable of towing mine countermeasures sleds. HM-12 was called into action after the 1973 truce in the Vietnam War. The squadron deployed to ships in the Tonkin Gulf, for Operation End Sweep, the clearing of mines from the harbors and coastal waters of North Vietnam. Mission complete, the Sea Dragons returned to Norfolk for transition to the RH-53D version, the first helicopter designed expressly for mine countermeasures.