USS Alacrity (AM-520/MSO-520) was an Ability-class minesweeper acquired by the United States Navy for the task of removing mines that had been placed in the water to prevent the safe passage of ships. The third ship to be named Alacrity by the Navy, MSO-520 was laid down on 5 March 1956 at Sturgeon Bay, Wisconsin, by the Peterson Builders, Inc.; launched on 8 June 1957; sponsored by Mrs. Henry J. Armstrong, the wife of Capt. Armstrong, the chief of staff and aide to the Commandant of the 9th Naval District; ferried to Boston, Massachusetts, via the Great Lakes and the St. Lawrence River; fitted out at the Boston Naval Shipyard; and commissioned there on 1 October 1958, Lt. Theodore W. Pstrak in command.