[1] The submarine was driven by a two-shaft diesel engine providing a total power of 480 horsepower (360 kW) and two electric motors each providing 620 horsepower (460 kW) power,[1] for a speed of 11 knots (20 km/h; 13 mph).

Post-H20 H-class submarines had ranges of 2,985 nautical miles (5,528 km; 3,435 mi) at speeds of 7.5 knots (13.9 km/h; 8.6 mph) when surfaced.

[4] The design was based on the Holland 602 type submarine, altered to meet Royal Navy specifications.

From 26 to 29 August 1939, the flotilla deployed to its war bases at Dundee and Blyth.

[6] Beginning on 22 March 1941, the Royal Navy and Allies began deploying submarines off Brest, France to prevent the German battleships Gneisenau and Scharnhorst from leaving port.