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	General characteristics (original design)
Displacement:	1,210 tons (surfaced) 1,760 tons (submerged)
Length:	274 feet 9 inches
Beam:	23 feet 1 inch
Draught:	16 ft
Propulsion:	Three shafts Surfaced – 3 x 12 cylinder diesel engines (3,600 hp) Submerged – 2 x battery driven electric motors (1,200 hp)
Speed:	19.5 knots (surfaced) 9.5 knots (submerged)
Range:	4,000 nautical miles (7,000 km) at 12 knots (22 km/h)
Complement:	5 officers, 40 seamen
Armament:	6 x 18-inch (457 mm) torpedo tubes (4 bow, 2 beam) 1 x 4-inch (102 mm) gun
Diving depth:	300 ft (91 m) max

The British J-class submarine was a First World War submarine designed as a counter to a perceived (but incorrect) threat from high speed German U-boats.

Reports that the Germans had submarines capable of speeds equal to that of surface vessels led to consideration of high-speed submarines by the Admiralty. The idea that submarines could keep up with and work alongside the surface fleet had already been attempted with the troublesome steam-powered K-class but the idea taken further even though the reported German boats were proved to be non-existent.

This resulted in a diesel-electric design that was unique within the Royal Navy. The submarines had three screws, which allowed them to reach a speed of 19.5 knots (36 km/h) on the surface - only a little short of the top speed of current battleships.

Eight boats were originally planned, this dropped to six before settling at seven which were built. These changes led to the original J7 and J8 becoming J3 and J4 in April 1915.

The first boat, HMS J4 was commissioned on 17 July 1916 and assigned to the 11th Submarine Flotilla at Blyth in Northumberland. It was joined by the others.

Thereafter the J-class submarines took part in activities against German surface vessels and German submarines both off the Tyne and Gibraltar. One boat, HMS J6 was sunk in 1918 by a British warship.

At the end of the war, the remaining six submarines were made a present to Australia and transferred to the Australian Navy in 1919. They were all transferred into the Australian reserve fleet at Westernport on 12 July 1922. The submarines were all scuttled in the mid-1920s onwards. Four of the submarines, the HMAS J1, J2, J4 and J5, were scuttled in Bass Strait, approximately 4 km WSW of the entrance to Port Phillip Bay, and are currently popular SCUBA diving sites. The remaining two submarines were scuttled as breakwaters inside Port Phillip Bay, with the J3 being scuttled near Swan Island in Queenscliff and the J7, the last of the submarines to be scuttled, at the Sandringham Yacht Club in 1930.

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British J class submarine

• Site on J class wrecks