Battle - class trawler Battle - class trawlers were naval trawler s built for and used by the Royal Canadian Navy ( RCN ) during the First World War . Between the wars , some remained in RCN service , but most were transferred to the Department of Marine and Fisheries , where they performed a number of functions , including working as lightships and fisheries patrol vessels . During the Second World War , a number of these trawlers were re - acquired by the RCN , but all the navy ' s Battle class trawlers were decommissioned soon after the war . A number of the class remained in civilian government and commercial service for years after the war , although most had been disposed of by the early 1960s . Origins and Military Service . The RCN ' s Battle class trawlers formed part of the Canadian naval response to Admiralty warnings to Canada about the growing German U - boat threat to merchant shipping in the western Atlantic . Intended to augment anti - submarine patrols off Canada ' s east coast , these ships were modelled on contemporary British North Sea trawlers , since the standard types of Canadian fishing vessels were considered unsuitable for patrol work . The resulting design was a - long vessel with a beam of about , a draft of around , and a top speed of , which made it roughly comparable to the Royal Navy ' s Castle class trawler s . The 12 - pounder gun that was the Battle class trawlers ' main armament was considered to be the smallest gun that stood a chance of putting a surfaced U - boat out of action , and they also carried a small number of depth charge s . Named after battles of the Western Front during the First World War , they were built by shipyards on the Great Lakes and St . Lawrence River at a cost of some $ 191 , 000 each , and entered service relatively late in the war . Between the Wars . The twelve trawlers remained in commission with the RCN until 1920 , and in early 1919 , three of them ( , , and ) accompanied on a trip to the west coast via the Panama Canal . In 1920 , nine of the class were transferred to the Department of Marine and Fisheries , where they served as buoy tenders , fisheries patrol vessels , and lightships , although one of the ships ( " Armentières " ) was soon returned to the RCN . became a buoy tender , while , , and " Givenchy " became fisheries patrol vessels . , , , and were converted to lightships . They remained in service with the Department of Marine and Fisheries throughout the interwar period , but a number were re - acquired by the RCN on the eve of the Second World War and returned to naval service . Three of the class ( , " Thiepval " , and ) were not transferred to civilian government service , and were rejoined by " Armentières " in 1923 . Remaining with the RCN throughout this time , they served as patrol and training vessels , and some were placed in reserve at various points . In 1924 , " Thiepval " undertook a lengthy trip across the North Pacific to the Soviet Union and Japan to support an ultimately unsuccessful British round - the - world flight attempt . Some six years later , " Thiepval " struck an uncharted rock in the Broken Islands of Barkley Sound on British Columbia ' s west coast , and sank . " Thiepval " was the first of the class to be lost , although " Armentières " had sunk and been salvaged in 1925 . Second World War . By 1939 , only one Battle class trawler , " Armentières " , remained in active naval service , although " Festubert " was in reserve and " Ypres " had just emerged from a refit to become a gate vessel for Halifax ' s anti - submarine defences . During 1939 , the RCN re - acquired five other members of the class : " Arleux " , " Arras " , " Loos " , and " St . Eloi " on the east coast , and " Givenchy " on the west coast . The east coast trawlers served primarily as gate vessels at Nova Scotia ports including Halifax and Sydney . In 1940 , the British battleship accidentally rammed and sank " Ypres " , but without loss of life . On the west coast , " Armentières " served as an examination vessel , while " Givenchy " served primarily as an accommodation ship . Post - War Fates . Following the Second World War , the trawlers that had served with the RCN were soon decommissioned and either sold or returned to civilian government service . Many were broken up in the 1950s or otherwise disposed of in the early 1960s , although two ( " Armentières " and " St . Julien " ) were still in existence in the 1970s , and their final fates remain unclear .