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] L7 was initially fitted with a 3inches anti-aircraft gun, but this was later replaced by a 4adj=onNaNadj=on deck gun.[5]
HMS L7 was built by Cammell Laird, Birkenhead. She was laid down in May 1916 and was commissioned in December 1917. She was based at Falmouth, Cornwall in 1918. She sailed with the Submarine Depot Ship to Hong Kong in 1919 as part of the 4th Submarine Flotilla, arriving there in January 1920. L7 was sold to Hughes Bolckow on 26 February 1930 for scrapping at Blyth.