HMS J7

HMS J7 (later HMAS J7) was a J-class submarine operated by the Royal Navy and the Royal Australian Navy.

Design and construction

The J class was designed by the Royal Navy in response to reported German submarines with surface speeds over 18 knots (33 km/h; 21 mph). The submarines had a displacement of 1,210 tons surfaced, but J7 had a lighter submerged displacement than her sister boats, at 1,760 tons. Each submarine was 275 feet (84 m) in length overall, with a beam of 22 feet (6.7 m), and a draught of 14 feet (4.3 m). The propulsion system was built around three propeller shafts; the J-class were the only triple-screwed submarines ever built by the British. Propulsion came from three 12-cylinder diesel motors when on the surface, and electric motors when submerged. Top speed was 19 knots (35 km/h; 22 mph) on the surface (the fastest submarines in the world at the time of construction), and 9.5 knots (17.6 km/h; 10.9 mph) underwater. Range was 4,000 nautical miles (7,400 km; 4,600 mi) at 12 knots (22 km/h; 14 mph).