During the Napoleonic Wars, a chain of coastal fortifications were built around the UK, with St. Catherine’s Island chosen as a site due to its prominence and proximity to the ports of Pembroke and Milford. Work began in 1867 and was completed in 1870, by the building contractor Mr. George Thomas of Orielton Terrace, Pembroke Dock. The fort was not fully armed for a further 16 years, by 1886 it had its full armament of 6 x 7inch R.M.L’s housed in the casemate areas of the gun deck and 3 x 9inch R.M.L’s on roof battery.
In 1907 the Island was sold privately for £500, and eventually by way of further sale, found its way into the hands of the wealthy Windsor – Richards family, who were involved in the South Wales Iron and Steel Industry. The elegance of their occupation is well remembered, with the main hall carpeted with animal skins, glass trophy cabinets, Tapestries, and many Stag heads and hunting trophies bedecking the walls. The principal rooms were furnished in period styles, with the main hall containing its huge open fireplace being a focal point for numerous lavish celebrations, in particular, the Tenby Hunt Ball. They also built a 2 bedroom summerhouse at the front of the island. When the house was compulsory purchased in 1940 the internal fittings were auctioned by Harrods and the catalogue still exists.
The fort was sold to a Tenby businessman in 1962 and in March 1968 the fort was turned into a zoo. The 10 year zoo period housed three different operators before eventually relocating in 1979. The fort has effectively stood empty since this time.