In 1704, the British took possession of Gibraltar and, by 1720, they had installed a pair each of 18-pounder and 12-pounder guns. By 1744, there were over 20 guns around Rosia Bay. Parson's Lodge Battery was originally named the 9th Rosia Battery. The Parson's Lodge name is first recorded in 1761 and reputedly refers to the dwelling of the parson of a church and hermitage named St. John the Green.
In early October 1840, Major-General John Thomas Jones arrived to inspect the defences of Gibraltar. He remained on the rock until June 1841, when he returned to England. Jones advised on improvements for Parson's Lodge Battery, which caused eight guns to be installed in 1842.
At the height of its military importance, the battery had three 10-inch rifled muzzle-loading guns that guarded the approaches to Rosia Bay, which is the only natural harbour on The Rock. The guns were installed in 1884. These guns fired a 400-pound shell over two and a half miles. Gibraltar Shields, which consisted of thick layers of iron around thick teak planks, protected the guns. The shields later used bolts that were also protected against abnormal loads as they included wooden bushes and had corners filed away to prevent them being snapped when resisting an enemy's shell.
Beneath the fort lies a narrow tunnel that at one time housed a one-metre gauge railway but which is now a road tunnel. The tunnel was one of two originally created to take large quantities of quarried stone from Camp Bay to the harbour's at South Mole when it was constructed in the 1880s.
The battery was used during both World Wars and, in 1941 it had anti-aircraft and anti-tank guns as well as anti-aircraft searchlights installed.
This fortification is now in the hands of the Gibraltar Museum who are currently using it as a research centre, for their cave and undersea studies.