Auxiliary Motor Minesweepers ( YMS ) Auxiliary Motor Minesweepers ( YMS ) were small minesweepers commissioned by the United States Navy for service during World War II . The YMS proved so successful as a type that it eventually became the basis for the AMS type of U . S . Navy minesweeper . Origin of the YMS . The Henry B . Nevins Shipyard , Inc . , at City Island , New York , designed the YMS and laid the keel of the first one , , on 4 March 1941 . Launched on 10 January 1942 , " YMS - 1 " was completed two months later on 25 March 1942 . From keel - layng to completion , the yard built " YMS - 1 " in only three months and 18 days . The “ Y ” designation . The first wooden minesweeper of this class was to gain prominence in all theaters during World War II . A total of 561 were built at various U . S . yards . 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 indcate 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 . Use as minesweepers . 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 . One of their greatest losses occurred on 9 October 1945 , when seven U . S . Navy YMSs were sunk in a typhoon off Okinawa . The wood - hulled YMS proved to be one of the U . S . Navys more durable and versatile types through a quarter - century of service , filling a variety of roles for a number of navies . Characteristics . All 481 ships of this type had the same general characteristics . The only significant variation within the type was one of appearance ; " YMS - 1 " through " YMS - 134 " had two stacks , " YMS - 135 " through " YMS - 445 " , " YMS - 480 " , and " YMS - 481 " had one , while " YMS - 446 " through " YMS - 479 " had none . History . 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 . A number of YMSs were transferred to other navies during or after the war . During Project Hula , the United States secretly transferred 31 of them to the Soviet Union between 17 May and 3 September 1945 , and some of these saw action in the Soviet Navy during Soviet military operations against the Japanese between 9 August and 5 September 1945 . The transfer of five more was canceled when transfers halted on 5 September 1945 . One , " T - 610 " ( ex - ) , sank in 1945 while in Soviet service , and the Soviet Union transferred two , " T - 605 " ( ex - ) and " T - 611 " ( ex - ) , to the People ' s Republic of China after striking them from the Soviet Navy list in 1955 ; during 1955 and 1956 the other 28 were scrapped by the Soviet Union or destroyed off its coast by mutual agreement between the two countries . Five YMSs served in the German Navy in different functions for tests , trials , and training ; all of them had a civilian crew and were decommissioned between 1975 and 1988 . " YMS - 327 " , the last YMS . , originally " YMS - 327 " , the last of her kind in U . S . service , was struck from the Navy List in November 1969 .