L52 and its successors were modified to maximise the number of 21-inch (53.3 cm) torpedoes carried in the bow. The submarine had a length of 235feet overall, a beam of 23feet and a mean draft of 13feet.[1] They displaced 960LT on the surface and 1150LT submerged. The L-class submarines had a crew of 44 officers and ratings.[2] They had a diving depth of 150feet.[3]
For surface running, the boats were powered by two 12-cylinder Vickers[4] 12000NaN0 diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 600hp electric motor. They could reach 17kn on the surface and underwater. On the surface, the L class had a range of 4200nmi at .[1]
The boats were armed with six 21-inch torpedo tubes in the bow. They carried eight reload torpedoes for a grand total of a dozen torpedoes.[5] They were also armed with two 4adj=onNaNadj=on deck guns.[2]
HMS L71 was laid down on 29 August 1917 by Scotts Shipbuilding and Engineering Company at their Greenock shipyard, launched on 17 May 1919, and completed on 23 January 1920.
On commissioning, L71 joined the 2nd Submarine Flotilla, based at Devonport.[6] The boat was sold for scrap on 25 March 1938 at Milford Haven.