The Royal Navy started to build replacements for the and sloops of the First World War, when the two vessels of the were laid down in 1928, with the similar four-ship laid down in 1929 and the eight ships of the being laid down in 1929–31. All of these ships were designed to combine the convoy-escort role of the Flower class with the minesweeping duties of the Hunt class, being fitted with equipment for both roles. By 1932, however, it became clear that what was needed was ships dedicated to a single role. Development therefore began of the s as a cheaper mass-production minesweeper, while a new class of sloops would be built that was more closely matched to the escort role. The new class of escort sloops, the Grimsby class, had a heavier gun armament than its predecessors, with two 4.7 inch Mark IX guns mounted fore and aft replacing the guns of the earlier ships. As the guns were low-angle guns, not suited to anti aircraft use, a single QF 3 inch 20 cwt anti-aircraft gun was mounted in "B" position. Four 3-pounder saluting guns completed the ships' gun armament. The ship was powered by two geared steam turbines driving two shafts, fed by two Admiralty 3-drum boilers. This machinery produced and could propel the ships to a speed of. Eight ships of the class were built for the Royal Navy, being laid down between 1933 and 1935 and completing between 1934 and 1936. The last two ships built for the Royal Navy, and had differing armaments, with Aberdeen replacing the 4.7 and 3-inch guns with two 4-inch anti-aircraft guns, and adding a quadruple.50 inch anti-aircraft machine gun mount, while Fleetwood had a main gun armament of two twin 4-inch anti-aircraft mounts, with close-in anti-aircraft armament of four.50 in machine guns. The Royal Australian Navy also adopted the Grimsby class, with two ships being laid down in 1934–35 and completed in 1935–36, with two more ships laid down in 1938–39 and completed in 1940. The first two ships were armed with three single 4-inch anti-aircraft guns, while the third and fourth ships having one twin and one-single 4-inch mount, with close in armament a quadruple machine gun mount in all four ships. The armament of most of the class was reinforced during the Second World War, with several gaining additional 4-inch guns, with the close in anti aircraft armament being supplemented by the addition of Oerlikon 20 mm cannon. The ships' depth charge complement increased from 15 at the start of the war to 40 for Australian ships and up to 90 for Royal Navy ships, while several ships were also refitted with a Hedgehog anti-submarine projector.
