Inchgarive Island has been fortified since at least 1490 when a castle was built here. During the building of the Forth Bridge in the 1880s, the Island was used to house workers and equipment.
The Island formed part of the Inner Defence Line of the Firth of Forth. By 1902 two 12-pdr Quick Fire guns had been mounted on the East end of the Island with supporting Defence Electric Lights. In 1915 these were replaced by four 4.7-inch Q.F. guns, which by 1917 had been downgraded to 12-pdr (18cwt) Q.F. guns. The 4.7-inch guns were mounted in two pair. On pair on the highest point of the Island, facing North East and the other pair a level below facing East. These 4.7-inch emplacements can still be clearly seen.
During World War I a garrison of forty one soldiers were on the Island.
The National Archives, Fort Record Book WO 192/100 from 1907 to 1927.