The Royal Commission on the Defence of the United Kingdom reported in 1860 and recommended a string of fortifications to protect the Bristol Channel. These included batteries or forts on Steep Holm, Flat Holm, at Brean Down and Lavernock Point.
Work on Steep Holm Island was carried out between 1866 and 1867. Fifty local and Irish Labourers were used and the facing stones were brought in from South Wales. All the building materials to build the barracks and batteries were winched up the cliff at South Landing and then hauled up to the contour path (about 200 feet). Limestone from Steep Holm itself was used for backing and infilling.
The rainwater collection was from the roof of the barracks and held in an underground reservoir with a capacity of 49,000 gallons.
Six separate gun batteries were built between 1866 and 1871 around the Island. Ten 7-inch Mark III RML guns of seven tons were mounted in 1871 (1882?). Two of these batteries, Rudder Rock and Tombstone, had a single gun while the remaining four batteries each had a pair of guns in separate barbette emplacements. Each battery had its’ own underground cartridge and shell stores. The Batteries built were at: