Palmerston Fort - Steep Holm

Both Steep Holm and Flat Holm were fortified in the 1860s as a defense against invasion. They form part of a line of defenses, known as Palmerston Forts, built across the channel to protect the approaches to Bristol and Cardiff.

The island was fortified following a visit by Queen Victoria and Prince Albert to France, where they had been concerned at 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 and the island formed part of this strategic coastal defence system. Construction began in 1865 and was completed in 1869.

Steep Holm has several gun batteries, some of which are Scheduled Ancient Monuments, and a centralized group of brick-built barrack blocks.

These facilities were updated in both World War I and World War II; in World War II, search light batteries were built on Steep Holm. The Steep Holm batteries were also connected, by underwater telegraph cable, to the Brean Down Fort batteries, but parts of the cable were stolen for scrap after the end of World War II.