Auxiliary motor minesweepers

Originally a class of "motor minesweepers" (MS), "Y" was added to distinguish them from other minesweeper types; sources disagree on whether "Y" stood for "yardcraft" – indicating a type of craft assigned for duty within a navy shipyard or naval base and not expected to go beyond waters adjacent to the base – or to indicate they were built by yacht-builders; YMSs were built at 35 yacht yards, rather than at larger shipyards, 12 on the United States East Coast, 19 on the United States West Coast, and four in yards on the Great Lakes.

Records show that YMSs were used in the United States Navy to sweep mines laid by enemy submarines as early as 1942 off the ports of Jacksonville, Florida, and Charleston, South Carolina.

Originally rated as service craft, they were used during World War II for inshore sweeping to prepare the way for amphibious assaults.

Surviving YMSs were reclassified as AMS in 1947, given names, and re-rated as mine warfare ships; in 1955 they received the new type symbol MSC(O), changed to MSCO in 1967.

These ships bore much of the mine warfare burden in Korea, formed a major portion of U.S. Navy minecraft strength through the 1950s, and provided underway training for Naval Reservists in the 1960s.

The U.S. Navy auxiliary motor minesweeper USS YMS-143 when new in February 1943. Secretly transferred to the Soviet Navy on 17 May 1945 during Project Hula , she became T-522 and took part in the Soviet conquest of the Japanese province of Karafuto on southern Sakhalin Island between 11 and 25 August 1945. T-522 served in the Soviet Navy until stricken in July 1956 and dismantled for spare parts. [ 1 ]