Garden Island is an inner-city locality of Sydney, in the state of New South Wales, Australia. It is located to the north-east of the Sydney central business district, north of the suburb of Potts Point.
Garden Island is the site of Fleet Base East of the Royal Australian Navy (RAN). Situated above Garden Island on the Potts Point ridgeline is HMAS Kuttabul, the RAN's administrative, training and logistics support establishment for the Sydney area, named after the converted ferry HMAS Kuttabul which was sunk near Garden Island in Sydney Harbour by a Japanese midget submarine in May 1942. Garden Island is the principal east coast naval base of the RAN, and home port to many of the RAN's major ships.
The northern part of the area is open to the public and is accessible via Sydney Ferries.
Garden Island was opened to the public for the first time in decades in November 2002.
Garden Island was originally an island in Sydney Harbour, but extension of the base and the construction of a dry dock in the channel between the island and the mainland have resulted in its connection to the mainland shore at Potts Point from the 1940s. The wharves of the naval base now stretch the length of the eastern side of Woolloomooloo Bay, from the suburb of Woolloomooloo to the end of the original island.
The tunnels were used to move guns from one side of the island to the other. There are also older tunnels that were used to transport ammunition. The tunnels are now used for electrical wiring and communications.
The island also has a pit that was built in the 1800s and was used as a storage facility in case the island was ever attacked. The entrance to this pit has now been sealed.