Alexandra Battery was recommended in the Jervois Report of 1865 to protect the Narrows Channel. This was to be a battery without any land defences or perimeter wall. The gun emplacements were for five 9-inch RML guns, four of these behind iron shields. The 9-inch RML on behind a masonry embrasure was on a dwarf carriage, the other four on casemate traversing carriages.These iron shields would be used extensively at this time in an attempt to protect the gun from incoming fire. Engineer Battery in Gibraltar is of a similar basic design.
The shields were made up of three wrought iron plates, two H beams supported the shield at both the top and bottom. Similar iron shields were used in numerous casemates positions such as Fort Bovisand and Hurst Castle.
Authority to commence the work was given on 8th March 1865 and work commenced in June 1865. The Battery was completed on the 1st December 1870. The total cost of the battery was £12,586, slightly under the estimated cost.
The Battery included accommodation for two NCOs, two cartridge stores, two expense shell stores, a side arm store, a main shell store, and Royal Artillery Store. Water was to be collected from the roof of the side arm shed and accommodation and collected in a 2250 galleon tank.
In about 1904 the battery was upgraded to mount two 6-inch Mark VII BL guns. Four of the original 9-inch gun emplacement were buried or destroyed in building the new emplacements, but the iron shielded emplacement on the East side of the battery has survived with the 9-inch RML gun. A Battery Command Post was built on the top of what had been an expense magazine on the Eastern extremity of the battery, and this remains with a DRF pedestal. The two 6-inch Mark VII BL guns on Mark VI mounts have also been left on site.