The Fairmiles played a vital role as escorts in the St. Lawrence River and the Gulf of St. Lawrence, and as escorts to convoys between Newfoundland and the mainland. They also carried out A/S patrol, port defence and rescue duties, releasing larger escort craft urgently needed elsewhere.

In 1942 it was decided to send two flotillas for the winter to the Caribbean, where the U-boats were enjoying great success owing to a shortage of U.S. escorts.

The 72nd and 73rd Flotillas, of six boats each, left Halifax in mid-December for Trinidad via Boston and other east coast ports. Stress of weather en route forced the 73rd Flotilla to return home after reaching Savannah, Georgia, but the boats of the 73rd Flotilla operated until the following spring out of Miami and Key West under the (U.S.) Commander, Gulf Sea Frontier. Their "mother ship" H.M.C.S. Provider was stationed at Key West. She also acted as base ship for the 70th and 78th Flotillas in Bermuda during the winter of 1943-44.

Early in June, 1943, M.L. 053 distinguished herself by recovering, intact, two mines of a barrage laid by U-119 in the Halifax approaches on June 1. M.L.s 052, 062, and 063 were transferred to the Free French Forces in February 1943, and stationed at St. Pierre and Miquelon under operational control of the Flag Officer, Newfoundland.

Most of the Fairmiles were sold at war's end, but half a dozen remained in service as training ships on the Great Lakes in the 1960s: Beaver (M.L. 106), Cougar (M.L. 104), Moose (M.L. 111), Raccoon (M.L. 079), Reindeer (M.L. 116), and Wolf (M.L. 062). A seventh, Elk (M.L. 124) served on the west coast. The animal names recalling those of the armed yachts whose duties the Fairmiles had taken over, were bestowed in 1954.

"B" Type M.L.s 053-111
Displacement: 79 Tons
Dimensions: 112' X 17'10" X 4'10"
Speed: 20 Kts.
Crew: 3 Officers, 14 Men
Designed Armament: 3 -20 mm

"B" Type M.L.s 112-129
Displacement: 79 Tons
Dimensions: 112' X 17' X 4'10"
Speed: 22 Kts.
Crew: 3 Officers, 14 Men
Designed Armament: 3 -20 mm