These wooden-hulled drifters were built along the same general lines as those of the RN. All were launched during 1917, and 37 of them are supposed to have been commissioned before the end of the war. They were intended for minesweeping and patrol duty, and 14 served at Gibraltar, 6 at Bermuda and 5 in West Africa from 1918 to 1919. A further 18 were lent to the USN during the same period. Like the TRs, they found ready employment as fishing vessels after the war, and a few served in the RN from 1939 to 1945. Three of the drifters, unnumbered were destroyed incomplete by fire at the Canada Steamship Lines plat at Sorel on June 19, 1917.