HMS J7 (later HMAS J7) was a J-class submarine built for the Royal Navy by HM Dockyard Devonport in Plymouth and launched on 12 February 1917. The submarine's layout differed from the other J class with the control room being placed behind the machinery spaces. This resulted in a changed external appearance with the conning tower further back compared to other members of the class. She was transferred to Australia on 25 March 1919 and operated out of Geelong.