Built at Collingwood, she was commissioned at Montreal on June 19, 1941, and arrived at Halifax on June 27 for final fitting-out. After working up, she arrived at St. John's on August 25 to Join Newfoundland Command, and on September 5 Sailed with Chambly for exercises. The two were ordered to reinforce the beleaguered convoy SC.42, which lost 18 ships, and just before joining on September 10, they surprised and sank U 501 astern of the convoy. Moose Jaw, which had rammed the U-boat, required ten days' repairs at Greenock, following which she arrived at Tobermory on October 1 to work up. For the next for months she operated between St. John's and Iceland, but in January, 1942, she arrived at Londonderry from SC.64, the inaugural "Newfie-Derry" convoy. On February 19, 1942, she ran aground on the south entrance of St. John's harbour en route to join convoy HX 176, and although re-floated soon afterward proved to be holed and leaking in several places. Temporary repairs were carried out at St. John's from February 20 to March 5, and permanent repairs at Saint John, N.B., from March 15 to June 25. Briefly assigned to WLEF, she was detached in September for duties in connection with Operation "Torch", and made here passage to the U.K. with convoy SC.107, which lost 15 ships to U-boats. During the next five months Moose Jaw was employed escorting U.K.-Mediterranean convoys, returning to Halifax on April 20, 1943. Refitted there, she joined Quebec Force at the end of May for escort duties in the Gulf of St. Lawrence, later transferring to Gaspé Force. She underwent a major refit, including fo'c's'le extension, at Liverpool, N.S., from December 19, 1943 to March 23, 1944. After working up in St. Margaret's Bay she left Halifax on May 1 for the U.K., to join Western Approaches Command, Greenock, for invasion duties. She served in the Channel until September, 1944, when she joined EG 41, Plymouth, and escorted coastal convoys from her base at Milford Haven until the end of the war. She left for home in May, 1945, was paid off at Sorel on July 8 and broken up at Hamilton in 1949.
Focsle Extended, Liverpool, NS, 23 Mar 44