Grimsby-class sloop

With the realisation that war was approaching, the 13 Grimsby-class sloops were laid down in the mid- to late-1930s. Of these eight were built in the United Kingdom for the Royal Navy, four in Australia for the Royal Australian Navy and one for India. Armament varied considerably between ships with the four Australian ships being similar to HMS Deptford (U53) but armed with an additional 4 in gun.

Losses during World War II were HMS Grimsby (U16), HMAS Yarra (U77) and HMAS Parramatta (U44). Some survivors of this class served into the 1960s.

Design
The Royal Navy started to build replacements for the Flower-class and Hunt-class sloops of the First World War, when the two sloops of the Bridgewater class were laid down, with the similar four-ship Hastings class laid down in 1929 and the eight ships of the Shoreham class 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 Halcyon-class minesweepers 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 in (120 mm) Mark IX guns mounted fore and aft replacing the 4-inch (102 mm) guns of the earlier ships. As the 4.7 inch 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 turbine driving two shafts, fed by two Admiralty 3-drum boilers. This machinery produced 2000 shp and could propel the ships to a speed of 16.5 kn.

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, HMS Aberdeen and HMS Fleetwood 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 in anti-aircraft machine gun mount, while Fleetwood had a main gun armament of two twin four 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 ship 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 90 for Royal Navy Ships, while several ships were also refitting with a Hedgehog anti-submarine projector.

First group

 * HMS Grimsby (U16) — built by Devonport Royal Dockyard, laid down 23 January 1933, launched 19 July 1933, completed 17 May 1934, bombed and sank off Tobruk 25 May 1941.
 * HMS Leith (U36) — built by Devonport, laid down 6 February 1933, launched 9 August 1933, completed 12 July 1934, sold into mercantile service 1946, to Royal Danish Navy as Galathea 1949. Sold for scrapping 1955.
 * HMS Lowestoft (U59) — built by Devonport, laid down 21 August 1933, launched 11 April 1934, completed 22 November 1934, sold into mercantile service 1946 and scrapped 1955.
 * HMS Wellington (U65) — built by Devonport, laid down 25 September 1933, launched 29 May 1934, completed 24 January 1935, hulked as mercantile headquarters ship 1947. This ship is still in existence and is permanently moored on the Thames Embankment in London.
 * HMS Londonderry (U76) — built by Devonport, laid down 11 June 1934, launched 16 January 1935, completed 20 September 1935, sold for scrapping 1948.
 * HMS Deptford (U53) — built by Chatham Royal Dockyard, laid down 30 April 1934, launched 5 February 1935, completed 20 August 1935, sold for scrapping 1948.

Second group

 * HMS Aberdeen (U97) — built by Devonport Royal Dockyard, laid down 12 June 1935, launched 22 January 1936, completed 17 September 1936, sold for scrapping 1949.
 * HMS Fleetwood (U73) — built by Devonport Royal Dockyard, laid down 14 August 1935, launched 24 March 1936, completed 19 November 1936, sold for scrapping 1959.

Royal Australian Navy

 * HMAS Yarra (U77) — built by Cockatoo Island Dockyard, Sydney, laid down 24 May 1934, launched 28 March 1935, completed 19 December 1935, sunk by Japanese cruisers JAPANESE CRUISER Atago and JAPANESE CRUISER Takao off Java 4 March 1942.
 * HMAS Swan (U74) — built by Cockatoo, laid down 1 May 1935, launched 28 March 1936, completed 10 December 1936, sold for scrapping 1965.
 * HMAS Parramatta (U44) — built by Cockatoo, laid down 9 November 1938, launched 18 June 1939, completed 8 April 1940, torpedoed by German U-boat U559 off Tobruk 27 November 1941.
 * HMAS Warrego (U73) — built by Cockatoo, laid down 10 May 1939, launched 10 February 1940, completed 21 August 1940, sold for scrapping 1966.

Royal Indian Navy

 * Indus — built by R. & W. Hawthorn Leslie & Company, Hebburn, laid down 8 December 1933, launched 24 August 1934, completed 15 March 1935, bombed by Japanese aircraft off Akyab 6 April 1942