Fort McNab is located on McNab’s Island and is the largest of the coastal defences batteries on the island. Authority to build the battery was given in November 1888 and work commenced on the site the following month. The Battery was completed on the 21st March 1892 at a cost of £24,000, slightly under budget. The Battery mounted two 6-inch BL guns and a single 10-inch RBL. There was a single 6-inch BL gun mounted on each of the flanks and the 10-iunch BL gun was mounted to the left of the Easterly 6-inch gun (this position still has a 10-inch gun in it). There were two magazines, the one on the left was shared between one of the 6-inch guns and the 10-inch gun. Fort McNab was designed as a counter bombardment battery to cover the approaches to Halifax Harbour.
The Fort included six casemates immediately behind the gun line including three barracks, a canteen, store, ablutions and boiler house. The Fort is also shown to have a Lookout House where the present Battery Command Post is and a Range Finding Pit.
In 1903 plans were drawn up for the coastal battery to be upgraded to two 9.2inch Mark X BL guns and two 6-inch Mark VII BL guns. (TNA WO 78/3963).
In 1905 it was decided to retain the original 10-inch BL in the Number 3 pit and and mount a new 9.2-icnh gun in the Number 4 pit. (TNA WO 78/3963). The underground magazine is shown as shared between the 9.2-inch gun and 10-inch gun, although with seperate shifting lobbies and hoists. This new 9.2-inch BL gun was mounted in 1906. Plans from 1905 show a Battery Command Post on the Western end of the traverser running along the gorge of the battery.
The 10-inch BL gun was later removed and used to be on display inside York Redoubt. It has now been moved back to Fort McNab and mounted in its’ original location. The adjacent gun emplacement for the 9.2-inch BL had a Battery Command Post built in it during World War 2 (1940-1).
In 1914 two Defence Electric Lights were mounted below the battery.
There was also a Position Finding Station constructed just to the East of the Battery and it is estimated that this was built about 1890.
A single 6-pdr Q.F. gun was also mounted on the ramparts of Fort McNab as a way of halting unidentified vessels approaching the harbour so they could be identified. These vessels would be held in the Examination Anchorage. This 6-pdr Q.F. gun was replaced in 1943 by a 75mm gun.
By 1919 the Battery was in mothballs, although a new barrel was mounted in 1921 for the 9.2-inch gun. In 1937 as war looked likely, For McNab was reactivated. Two new counter-bombardment were to be built, Devils Battery at Hartlen Point and Cambridge Battery at Chebucto Head. The 9.2-inch gun from Fort McNab was to be used at Devils Battery. Fort McNab was to retain its two 6-inch BL guns, although they were replaced by similar guns from Quebec City. The original guns having been sent to West Canada for coastal defence. In 1944 these 6-inch BL guns were again replaced by more modern guns of a similar calibre that were moved from Sandwich Battery.
In 1945 a radar was mounted within Fort McNab.
The last change came in 1953 when the two 6-inch BL guns were replaced by a single twin 4-inch naval gun. The Fort was decommissioned in 1960