During the later half of the 19th Century, Cardiff and Bristol had been protected by a line of coastal defence batteries covering the Bristol Channel from Lavenock in Wales to Brean Down Fort in England. Flat Holme and Steep Holme Island covered the intervals.
By the 1900 Cardiff was protected by Lavenock Battery with two 6-inch Mark VII BL guns, and Penarth Head Battery with two 12-pdr Q.F. guns. The 1905 report into the Defence of Commercial Ports recommended that both batteries be retained with their existing armaments. There were two defence electric lights at Lavernock Battery.