The TR series were minesweeping naval trawlers built during World War I. Ordered by the Royal Navy, they were loaned to the Royal Canadian Navy for seaward defence of the East Coast of Canada. The total number of vessels that entered service is unknown with 60 hulls constructed by eight Canadian shipyards. Based on the British Castle class, some entered service with the United States Navy during the war. Following World War I, they were sold for commercial use to replace the fishing vessels lost during the war. In World War II many of them were taken over by the Royal Navy as auxiliary minesweepers and two of them returned to the Royal Canadian Navy.