Fortifications developed on McNabs Island represent one element of a system of defences that have evolved around Halifax Harbour since the founding of Halifax in 1749. These fortifications include Citadel Hill (1749), Georges Island (1750), Point Pleasant (1762), York Redoubt (1793) and several defensive works on McNabs Island, beginning with Sherbrooke Tower, constructed on the seaward tip of Maugher Beach between 1815 and 1828. Later fortifications constructed on McNabs Island included Fort Ives (completed in 1870), Fort McNab (completed in 1892), Hugonin Battery (1899) and Strawberry Battery (1940). This evolving series of fortifications, later to become known as the Halifax Defence Complex or System, was to serve Halifax well over the years.

In 1965, the Historic Sites and Monuments Board of Canada declared that Halifax was "one of the four principal naval stations of the British Empire during the 18th and 19th centuries and as such was "of great national significance to Canada." The Board further indicated that the Halifax Defence System was unique on the North American Continent, containing as it does a complete conspectus of shore defences from the 18th century to the Second World War. To ensure the survival of the Defence System the Board recommended that representative examples of this compendum be protected. Fort McNab was to be preserved because of its important historical background and impressive extant resources.

For the most part, the fortifications on McNabs Island were maintained by the British until 1906 when the British garrison withdrew from Halifax. This is especially true for those forts constructed after 1865. Prior to this time some may have been manned by local militia members. Following the withdrawal of British troops, the fortifications on McNabs Island were infrequently manned except during both World Wars.