The Castle-class minesweeper was a highly seaworthy naval trawler adapted for patrol, anti-submarine warfare and minesweeping duties and built to Admiralty specifications. Altogether 197 were built in the United Kingdom between 1916 and 1919, with others built in Canada, India and later New Zealand. Many saw service in the Second World War.
Naval trawlers are vessels built along the lines of a fishing trawler but fitted out for naval purposes; they were widely used during the First and Second World Wars. Some—known in the Royal Navy as "Admiralty trawlers"— were purpose-built to naval specifications, others adapted from civilian use. Fishing trawlers were particularly suited for many naval requirements because they were robust vessels designed to work heavy trawls in all types of weather, and had large clear working decks. A minesweeper could be created by replacing the trawl with a mine sweep. Adding depth charge racks on the deck, ASDIC sonar below, and a 3-inch (76 mm) or 4-inch (102 mm) gun in the bow equipped the trawler for anti-submarine duties.
The ST Leukos was an Irish commercial trawler that was sunk off the coast off the north coast of Ireland by a German U-boat on 9 March 1940. The vessel, which had been fishing in the company of British trawlers, was attacked by the German submarine U-38 off Tory Island. The submarine surfaced opening fire with its deck gun. All 11 crew members were lost.
USS James (SP-429) — also known as USS W. T. James (SP-429) — was a steam trawler acquired by the United States Navy during World War I. She was converted into an armed minesweeper and assigned to the European Theater, where she performed varied tasks, including minesweeping, patrolling, and escorting of larger ships in convoy. In 1919, while returning to the United States, she was severely damaged in a storm off the French coast, and sank. Her crew were rescued.
HMT Firefly was a minesweeping trawler that saw service during the Second World War.
SM UB-18 was a German Type UB II submarine or U-boat in the German Imperial Navy during World War I. The U-boat was ordered on 30 April 1915 and launched on 21 August 1915. She was commissioned into the German Imperial Navy on 11 December 1915 as SM UB-18. The submarine sank 128 ships in 31 patrols for a total of 130,841 GRT and 725 tons, making her the 17th most successful U-boat in both world wars. UB-18 was rammed by the trawler Ben Lawer and sunk in the English Channel at 49°17′N5°47′W on 9 December 1917.
A naval drifter is a boat built along the lines of a commercial fishing drifter but fitted out for naval purposes. The use of naval drifters is paralleled by the use of naval trawlers.
SS Monte Nevoso was a cargo steamship that was launched in 1920 in England, owned in Italy, and wrecked in 1932 in the North Sea off the coast of Norfolk.
HMAS Goorangai was a 223-ton auxiliary minesweeper of the Royal Australian Navy (RAN). She was built in 1919 for the Government of New South Wales, then sold in 1926 to the fishing company Cam & Sons. The trawler was requisitioned for military service following the outbreak of World War II, converted into a minesweeper, and assigned to Melbourne. She was sunk in an accidental collision with MV Duntroon in 1940, becoming the RAN's first loss of World War II, and the first RAN surface ship to be lost in wartime.
HM Trawler Agate was purchased by the Royal Navy in 1935. She was modified from a trawler to be used to carry out anti-submarine work. In 1941 she was with the maintenance reserve at Rosyth, but in August was part of the Royal Navy's escort flotilla with convoy FS559 when she ran aground, becoming a total loss, on Haisborough Sands on 6 August with a loss of sixteen crewmen.
Davara was a British steam fishing trawler. Launched in 1912, it was requisitioned in 1914 by the Royal Navy for service in World War I and fitted out as a minesweeper. She was returned to her owners after the war and began service as a trawler once more.
HMAS Durraween (F93) was an auxiliary minesweeper operated by the Royal Australian Navy (RAN) during World War II. The ship was built as a trawler by Collingwood Shipbuilding Company at Collingwood, Ontario, Canada, and launched in 1918 as Seville. The ship served briefly in the Royal Canadian Navy during the last months of World War I, before being laid up and sold to a British company. In 1928, she was sold to Sydney-based fishing company and operated in Australian waters until she was requisitioned by the RAN in mid-1940 for use as an auxiliary minesweeper during World War II. Durraween operated in the Bass Strait as part of Minesweeping Group 54, and was responsible for clearing mines laid by German merchant raiders, and then later operated around the Torres Strait. She was returned to civilian service after paying off in late 1945, and was broken up in 1952.
HMT Richard Bacon (FY3587) was a British Castle class naval trawler completed in 1918. She served through both world wars under two different names and also had a lengthy career as a civilian fishing trawler. For a short while, she functioned as a support vessel for a famous transatlantic flight by a group of Italian bombers. She was scrapped in 1954 after her boiler failed during a storm.
HM Trawler Alvis was a British trawler that was taken up from trade and used by the Royal Navy during the Second World War. She was returned to the fishing industry at the end of hostilities in 1945.
HMCS Bras d'Or was an auxiliary minesweeper that served in the Royal Canadian Navy (RCN) between 1939 and 1940, when she sank with all hands in a storm. Previous to her service in the RCN, she served as Lightship No. 25 in the Canadian Department of Marine and Fisheries.
Preußen was a fishing trawler requisitioned during World War II by the Kriegsmarine for use as a Vorpostenboot. She was built in 1930 as August Wriedt, and was renamed Preußen in 1933. On 13 August 1944, she was sunk off Langeoog by Bristol Beaufighter aircraft of 254 Squadron, Royal Air Force.
Caldew was a British steam fishing trawler. Launched in 1914 as Maristo, she was requisitioned by the Royal Navy for service in the First World War the following year. Maristo survived the war and resumed trawling for the next two decades, being renamed Caldew in that time. She collided with fellow trawler Ospray II in 1935, sinking the latter ship.
United Kingdom Navy 
