The greater length of the Castles gave made them better seaboats than the Flowers, which were not originally designed for ocean escort work.

Large numbers (96 in total) were ordered in late 1942 and early 1943 from shipyards in the United Kingdom and Canada, but Allied successes in the Battle of the Atlantic meant that the requirement for escorts was reduced, and many ships (including all the Canadian ones) were cancelled.

[4] Two Admiralty Three-drum water tube boilers fed steam to a Vertical Triple Expansion Engine rated at 2,750 indicated horsepower (2,050 kW) which drove a single propeller shaft.

[4] 480 tons of oil were carried, giving a range of 6,200 nautical miles (7,100 mi; 11,500 km) at 15 knots (17 mph; 28 km/h).

[8][9] In 1948, Oakham Castle joined the 2nd Training Squadron based at Portland Harbour, continuing to serve in this duty until December 1950, when she was reduced to reserve at Devonport.