Bare Island Fort was built as a result of a visit in 1877 by Major-General Sir William Jervois and Colonel Peter Scratchley of the Royal Engineers to New South Wales to advise on coastal defences. Bare Island Fort on La Perouse Island was recommended along with Fort Scratchley in Newcastle. The fort was built between 1881 and 1889.
The fort was armed with two 9-inch RML guns, two 80-pdr RML and a single 10-inch RML gun in an armoured casemate. There were also two Nordenfelt Quick Fire Guns. The guns were laid out in a circle running round the island and linked by an underground walkway.
The fort made extensive use of concrete, although it appears to have had some problems with the local contractors. The only access to the fort was by zip line or boat until a bridge was built.