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 but armed with an additional gun . Losses during World War II were , and . Some survivors of this class served into the 1960s . Design . The Royal Navy started to build replacements for the " Flower " - class and " Hunt " - class sloop s 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 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 , 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 .