HMS J2

HMS J2 (later HMAS J2) 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 kn. They had a displacement of 1,210 tons surfaced, and 1,820 tons submerged. Each submarine was 275 ft in length overall, with a beam of 22 ft, and a draught of 14 ft. 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 kn on the surface (the fastest submarines in the world at the time of construction), and 9.5 kn underwater. Range was 4,000 nmi at 12 kn.

Armament consisted of six 18-inch (450 mm) torpedo tubes (four forward, one on each beam), plus a 4-inch deck gun. 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. 44 personnel were aboard.

J2 was built for the Royal Navy by HM Dockyard at Portsmouth in Hampshire and launched on 6 November 1915.

Operational history
J2 torpedoed and sank the German submarine SMU U-99 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. To this end, they offered the six surviving submarines of the J-class to the Royal Australian Navy as gifts. 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 HMAS Sydney (1912) and HMAS Brisbane (1915), and the tender HMAS Platypus (1917). The flotilla reached Thursday Island on 29 June, and Sydney on 10 July. Because of the submarines' condition after the long voyage, they were immediately taken out of service for refits.

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.

Fate
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 -38.31361°N, 144.58°W.

The J2 wreck, also known as "39 Metre Sub", "130 Foot Sub", "Broken Sub" or "Deep Sub", is submerged in 39 m 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.