St Martin’s Battery is on the southern edge of the Western Heights overlooking the dockyard. The battery was built between 1871 and 1874 to mount three 10-inch RML guns. These guns remained in place until at least the end of the century, with a new magazine being built into the cutting to the rear of the battery in 1890. This magazine was extended during 1940 to provide a network of tunnels as protection from German air raids.
There was a proposal to convert this to a High Angle Fire Battery, but nothing appears to have been done.
With the introduction of Breech Loading guns this battery became redundant, and it was probably replaced by South Front Battery with three 6-inch BL guns in 1903.
The Battery was extensively revised in 1940 with two 6-inch BL gun emplacements being built over the old RML emplacements.