HMAS Platypus is a former Royal Australian Navy (RAN) submarine base, located at 118 High Street, North Sydney with moorings in Neutral Bay, a suburb of Sydney in New South Wales, Australia. It was located upon the site of the Royal Australian Navy Torpedo Maintenance Establishment (RANTME), it built on the site of the former North Sydney Gas Works that operated on the site from 1877 and resumed by the Commonwealth in 1942. The Fleet Intermediate Maintenance Activity (FIMA) Workshops building on the site was originally used for torpedo assembly and storage during World War 2. It was later modified for submarine maintenance and repair, with a steel tower added to the northern end of the building for testing, cleaning and maintenance of periscopes.