The main armament of the fort was mounted on the ramparts. These high earth banks sweep round from east to west in a D shaped series of gun emplacements and firing steps. The armament mounted on the concrete circular emplacements consisted of 64pr. Rifled Muzzle Loading guns as the long range defence weapons. These could achieve a range of 4,000 yards with a full service charge of 8lbs of black powder.
To supplement the fire of these guns at the salient angles huge concrete pits held 7-inch RBL guns on Moncrieff disappearing mountings. Three were mounted in Fort Nelson.
On the main North rampart high angle fire was achieved by 6.6-inch RML howitzers some on travelling siege platforms and others on static howitzer beds.
Flanking fire was provided by 7-inch Rifled Breech Loading guns on the east and west ramparts where they crossed fire with the guns in the adjoining forts, Wallington and Southwick. It was this system of interlocking fire that made the line of forts on Portsdown a formidable deterrent, preventing an enemy from securing a foothold on the hill from where they could bombard the Dockyard. Two guns on each flank were placed in Haxo casemates, which provided overhead cover for the gun crews.
The guns on the ramparts were provided with expense magazines for storage of shells and cartridges.
Download a data sheet on the Armament of Fort Nelson