USS Leader (AM-490/MSO-490) was an Aggressive-class minesweeper acquired by the U.S. Navy for the task of removing mines that had been placed in the water to prevent the safe passage of ships. Leader (AM-490) was laid down by J. M. Martinac Shipbuilding Corp., Tacoma, Washington, 22 September 1953; launched 15 September 1954; sponsored by Mrs. Norman Wordlund; reclassified MSO-490 7 February 1955, and commissioned 16 November 1955, Lt. Comdr. Harvey E. Toponce in command. This MSO class of minesweeper was constructed of non-magnetic materials, including a wooden hull and aluminum engines, and had a degaussing system to reduce the magnetic field of the vessel, so that it could move over magnetic mines without detonating them. It was equipped with a "magnetic tail", two thick cables spooled