See main article: British J-class submarine. The J class was designed by the Royal Navy in response to reported German submarines with surface speeds over .[1] They had a displacement of 1,210 tons surfaced, and 1,820 tons submerged.[1] Each submarine was in length overall, with a beam of, and a draught of .[1] The propulsion system was built around three propeller shafts; the J-class were the only triple-screwed submarines ever built by the British.[1] Propulsion came from three 12-cylinder diesel motors when on the surface, and electric motors when submerged.[1] Top speed was on the surface (the fastest submarines in the world at the time of construction), and underwater.[1] Range was at .[1]
Armament consisted of six 18-inch (450 mm) torpedo tubes (four forward, one on each beam), plus a 4-inch deck gun.[1] Originally, the gun was mounted on a breastwork fitted forward of the conning tower, but the breastwork was later extended to the bow and merged into the hull for streamlining, and the gun was relocated to a platform fitted to the front of the conning tower.[1] 44 personnel were aboard.[1]
J2 was built for the Royal Navy by HM Dockyard at Portsmouth in Hampshire and launched on 6 November 1915.[2]
J2 torpedoed and sank the German submarine between the Orkney Islands and Norway on 7 July 1917.
After the war, the British Admiralty decided that the best way to protect the Pacific region was with a force of submarines and cruisers.[1] To this end, they offered the six surviving submarines of the J-class to the Royal Australian Navy as gifts.[1] J1 and her sisters were commissioned into the RAN in April 1919, and sailed for Australia on 9 April, in the company of the cruisers and, and the tender .[1] The flotilla reached Thursday Island on 29 June, and Sydney on 10 July.[1] Because of the submarines' condition after the long voyage, they were immediately taken out of service for refits.[1]
Apart from local exercises and a 1921 visit to Tasmania, the submarines saw little use, and by June 1922, the cost of maintaining the boats and deteriorating economic conditions saw the six submarines decommissioned and marked for disposal.[1]
The submarine was paid off on 12 July 1922. J2 was sold on 26 February 1924. She was scuttled in the ship graveyard off Port Phillip Heads at -38.3136°N 144.58°W.
The J2 wreck, also known as "39 Metre Sub", "130 Foot Sub", "Broken Sub" or "Deep Sub", is submerged in 39m (128feet) of water. The wreck lies on its keel running north–south with its bow pointing out to sea. During its scuttling the bow section broke off, exposing the forward torpedoes tubes and bow modifications. The wreck is accessible by experienced divers, but it is the deepest and most difficult of the four J-class submarine wrecks in the area.