McNabs Island, approximately five kilometres long by about 1.5 kilometres wide, is situated near the mouth of Halifax Harbour. Built between 1888 and 1892, Fort McNab is strategically situated at the south end of McNabs Island. For three-quarters of a century Fort McNab served as a gun battery and as the gatekeeper of Halifax Harbour. From the days of John A. MacDonald until the days of John Diefenbaker, Fort McNab guarded the outer channels to the harbour. Through two world wars it housed the port's Examination Station and was responsible for the crucial task of checking ships to ensure that they did not pose a risk to port security.
Fort McNab was decommissioned in 1959 and ownership was transfered to Parks Canada.