As Portland Harbour grew in importance and became the main base for the Channel and later the Atlantic fleets, so Nothe Fort remained an important element in the defences of the naval base.
With the advent of breach loading (BL) guns the 12 riffle muzzle loaded (RML) cannons were removed and 3x 6 inch guns were emplaced on the Ramparts. These new guns had a greater accuracy and better rate of fire than the 12 muzzle loaded guns. The armour piecing shell of the 6 inch gun weighed 100 pounds and had a range of 10 miles.
In order to accommodate the 6 inch guns it was necessary to undertake extensive structural work to support the weight of these guns on the Ramparts. In addition to the structural work a considerable amount of earthworks was undertaken to protect the guns from enemy fire. In order to convey the shells and cartridges from the magazines to the gun emplacements a series of hoist were installed