Time Out says
This small Harbour Island was named because of its original ‘spectacular’ shape – two small islands joined by a narrow peninsula. Sitting just behind Cockatoo Island, Spectacle was first used in 1865 as a storage site for the colonial government’s gunpowder. The Royal Australian Navy took over in 1913, and the island was used for shell-filling and munitions storage during the First and Second World Wars and then later as a Naval Repository.
Island hop? The island is now a fully functional naval base and not open to the public. But you can see historical items from the island at the Naval Heritage Centre, located on Garden Island.