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The L and M class was a class of sixteen destroyers of the Royal Navy, launched in 1939–1942.
L class The L class (also known as the Laforeys) were approved under the 1937 Naval Estimates.
Their design and armament was the subject of major debate as the proponents of heavier anti-aircraft armaments for such vessels were at last beginning to be listened to at the Admiralty, mainly as a result of the lessons of the Spanish Civil War.
They had single funnels as per the J class, a tripod foremast and a short mainmast just aft of amidships.
As ordered the class comprised a leader and 7 destroyers. Each ship was to mount 6 x 4.7 inch guns and 8 torpedo tubes. Close range armament had still to be decided, with the expected time to delivery being a crucial factor.
They were the first British destroyers to have their guns in fully enclosed mountings. They also continued the practice introduced in the Js of the leader Laforey being almost indistinguishable from the rest of the class, having only a more extensive cabin accommodation and better W/T equipment.
Main Armament As ordered the ships were to have six Mark XI 4.7 inch guns in Mark XX twin mounts. They were to be in 'A', 'B', and 'X' positions. 'X' mount was especially interesting in that it gave an arc of fire of around 320 degrees at low elevations and 360 degrees at elevations above around 20 degrees (estimated figures).
The Mark XX mount was fully enclosed and supposedly weatherproof. Their crews found that they were not. It also allowed the guns to be elevated independently.
The Mark XI gun was a major improvement on the previous version in that it threw a 62 lb shell (as opposed to the 50 lb in the preceding 'J's). It was also capable of being elevated to 50 degrees (40 for previous marks). Having said that the Japanese Navy had already introduced a 5 inch gun with 70 degree elevation to service as had the United States Navy so the 50 degrees of the 4.7 was by no means good, especially for anti-aircraft use. Why British designers had so much trouble has never been made clear, especially as the 4.5 inch fitted to Ark Royal were already in service and capable of elevations of 70 degrees plus.
As originally ordered they had no close-range armament at all as the various departments could not agree on what to fit ! Arguments as to one or two 4-barrelled pom-poms, one pom-pom and one of the 0.661 inch multiple machine guns then in development, one pom-pom and the traditional 0.5 inch machine gun raged around stoked by the manufacturing schedules (a second pom-pom per ship would not be available until 1942), the poor performance of the development models of the 0.661 and the campaign by a number of younger officers (led by Lord Louis Mountbatten) as to the effectiveness of all three weapons. Eventually development of the 0.661 was dropped as it clearly would not be available and effective in a sensible timescale, this simplified the arguments somewhat.
The outbreak of war focussed minds somewhat. Apart from the AA armament issue concerns started to be raised about progress generally. By February 1940 the two factors led to a proposal to change the design of four of the 'L's and fit a main armament of 4 inch Mark XVI* guns in Mark XIX High Angle /Low Angle (HA/LA) twin mounts as used as secondary armament in the Southampton-class cruisers already in service and main armament in the Black Swan class of sloops then under construction. Associated changes were dropping of the pom-poms altogether and provision of two quad 0.5 inch machine guns.
The lessons of the Norwegian campaign and Dunkirk drove home the need for this change and it was agreed in July 1940, there were also to be four of the twin mounts instead of the originally proposed three. The fourth was to be at the forward end of the after superstructure which cut down on the fire arcs of both mounts but ensured the fourth would still be available for use in heavy weather.
Not all senior officers were in favour, and some openly expressed opinions that it would mean the ships could not successfully fight their foreign equivalents. Experience in the Meditteranean, especially that of Force K which contained two of the 4-inch 'L's, made a mockery of the idea, with the reduced weight of each shell being compensated for by the much higher rate of fire.
Review of AA armament continued, and in October a decision was taken to remove the after bank of four torpedo tubes and fit a single 4-inch HA gun instead, and that is how the 4.7 inch gunned ships eventually got to sea.
L-class ships
M class | 
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