The L-class boats were enlarged and improved versions of the preceding E class. The submarine had a length of 231feet overall, a beam of 23feet and a mean draft of 13feet. They displaced 891LT on the surface and 1074LT submerged. The L-class submarines had a crew of 35 officers and ratings.[1]
For surface running, the boats were powered by two 12-cylinder Vickers[2] 12000NaN0 diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 600hp electric motor.[1] They could reach 17kn on the surface and underwater.[3] On the surface, the L class had a range of 3200nmi at .[1]
The boats were armed with a total of six 18-inch (45 cm) torpedo tubes. Four of these were in the bow and the remaining pair in broadside mounts. They carried 10 reload torpedoes, all for the bow tubes.[4] They were also armed with a 4adj=onNaNadj=on deck gun.[5]
HMS L3 was laid down on 19 October 1916 by William Beardmore and Company at their Dalmuir shipyard, launched on 14 January 1918, and completed on 3 July 1918. She was based at Falmouth, Cornwall in 1918.
HMS L6 was assigned to the 4th Submarine Flotilla and in 1919 and sailed to Hong Kong, arriving on 14 April 1920.
HMS L6 was sold for scrap in January 1935 in Newport, Monmouthshire.