The post war period, the Navy required no new destroyers or leaders, as so many were completed at wars end. For any new destroyers, one thing the designers had to take into consideration, was the increasing gun sizes being put aboard destroyers by the major powers. The Germans had put 5.9" guns aboard four V & S class destroyers, and these ships went to the Unites States, Great Britain, France and Italy as war reparations. Those countries had the chance to test these ships to destruction to see if they were as good as the hype that had surrounded them. The unanimous decision was that the 5.9"/6" gun size was too unwieldly for use on a destroyer. A destroyer armed with 5.9" would have a very low rate of fire, as trying to load 100+ pound shells on a deck, moving as much as a destroyer does, was not a good idea. (A lesson the Germans did not seem to have learnt as they put 5.9" aboard the Z series in the late 1930's) The French put a 5.5" gun aboard their Large Destroyers (Contre-torpilleurs) and produced some of the fastest destroyers ever produced. The Le Fantasque and Mogador class ships being outstanding examples. BUT, the general French destroyer was armed with a 5.1"/130mm gun. The United Kingdom went to the 4.7"/4.5" gun sizes, the United States settled on the 5" in various models. Japan initially followed the UK with a 4.7", which was replaced with the 5" gun through to the Akizuki class with its new model twin 3.9". Greenland settled on the 5" gun as main armament for its destroyers. Those ships built during the 1920's trough to 1933/34 version had low angle 5" gun with little AA value. Those built after 1934 had the new dual purpose guns. The older ships were supposed to go through a rebuild process from 1940 onwards (after the 4" destroyer refits) but with the war intervening this rebuild never took place, and they fought with what they had.
The new ships took the hull of the Amethyst class and replaced the 5x4" with 4x5" and also had space for the new quad 40mm AA guns. That mounting was to be the main AA weapon aboard ship. The triple sets of torpedoes were retained. The other new feature was a 20mm auto-cannon that replaced the old 15mm machine guns. Being of a size with the Amethyst class destroyer leaders, gave rise to the thought that the ships would be able to provide a 'Leader' from within the group. This did not work in practice as the changes in layout to the bridge structure and other accommodation factors meant there was no room for Captain 'D' and crucially his staff. These ships had not been designed as leaders and required a leader be provided for them to make up a flotilla.
Because of the low angle (50 degree) guns, these ships were kept away from enemy coast lines as much as possible. This put the ships on the North and South Atlantic convoy routes, with some even going on to operate in the Indian Ocean on the South Africa to Australia, or, to Port Said through the Red Sea/Suez Canal. Because of this type of service, most of the ships lost, first, 'Y' turret so that more depthcharges could be fitted, then the aft set of torpedoes were removed to offset topweight from the addition of electronics, then 'A' gun was removed and replaced with a Hedgehog ASW mortar. While reduced to 2x5" for the main armament, it was felt this would be more than enough to cope with a surfaced U-boat. The drawing above shows the lead ship Topaz in its final outfit in, before being lost to a German 'Gnat' torpedo in November 1943 while escorting a North Atlantic Convoy.
