HMS L12 was a L-class submarine built for the Royal Navy during World War I.

[2] For surface running, the boats were powered by two 12-cylinder Vickers[3] 1,200-brake-horsepower (895 kW) diesel engines, each driving one propeller shaft.

On the surface, the L class had a range of 3,800 nautical miles (7,000 km; 4,400 mi) at 10 knots (19 km/h; 12 mph).

[4] The boats were armed with four 21-inch torpedo tubes in the bow and two 18-inch (45 cm) in broadside mounts.

The boat collided with the submarine HMS H47 off Milford Haven, Wales on 9 July 1929.