 Flat Holm was fortified in the 1860s following a visit by Queen Victoria and Prince Albert to France, where they had been concerned by the strength of the French Navy. The Royal Commission on the Defence of the United Kingdom, under direction of Lord Palmerston, recommended fortification of the coast in 1865. The defences on the island, which became part of a line of defences known as the Palmerston Forts, were completed in 1869.
