HMS J3, Naval submarine wreck in Port Phillip Bay, Australia

HMS J3, a J-class submarine built for the Royal Navy, lies scuttled off Swan Island in Port Phillip at 38.244075°S 144.70305°E. The 275-foot boat had a beam of 22 feet and displaced 1,210 tons surfaced. Its triple-screw arrangement was unique among British submarines.

HMS J3 was built at Pembroke Dockyard in Wales and launched on 4 December 1915. In April 1919 the Royal Navy gifted six surviving J-class submarines, including J3, to the Royal Australian Navy; they sailed for Australia on 9 April with the cruisers Sydney and Brisbane and the tender Platypus, reaching Sydney on 10 July. J3 was paid off on 12 July 1922, sold in April 1924 and scuttled off Swan Island in 1926.

The six J-class boats were handed to the Royal Australian Navy as gifts in April 1919 and sailed from Britain with the cruisers Sydney and Brisbane and the tender Platypus, reaching Sydney on 10 July. Locals know the wreck off Swan Island as a dive site, and its propellers are kept at the Queenscliffe Maritime Museum.

The shallow depth and protected location of the wreck make it an accessible diving site for beginners exploring Port Phillip Bay's underwater heritage.

J3 was sold in April 1924 and scuttled off Swan Island in Port Phillip in 1926, at 38.244075°S 144.70305°E. Divers can still locate the hull at that position, near the Queenscliff side of the bay.