HMS L1 was the lead boat of the L-class submarines built for the Royal Navy during World War I.

[1] For surface running, the boats were powered by two 12-cylinder Vickers[2] 1,200-brake-horsepower (895 kW) diesel engines, each driving one propeller shaft.

[3] On the surface, the L class had a range of 3,200 nautical miles (5,900 km; 3,700 mi) at 10 knots (19 km/h; 12 mph).

[5] Originally laid down by Vickers, Barrow, as E-class submarine E57 on 18 May 1916, she and sister ship E58 incorporated enough changes that they were renamed as the first pair of boats of a newly designated L class.

While being towed to Newport she broke free and was stranded at Penanwell Cove, near Porth Nanven in Cornwall.