Fort Grey was originally a small castle, Chateau de Rocqauine. In 1803 the remains of the chateau were levelled and a battery built on this small island. The battery could hold about thirteen guns within a circular wall that was about 10 feet thick. There was at this time no gateway in the wall, and access was by step ladder.
In 1804 a Martello Tower was built within the enceinte, functioning much like a keep. A 24-pdr SB carronade was mounted on the top of the tower by 1816 and the battery mounted six 24-pdr SB guns.
The original magazine was built outside the battery wall and can still be seen. In 1809 and new magazine was built inside the Fort Grey walls, and this building was sunk partially underground.
Fort Grey is now the Shipwreck Museum, see https://museums.gov.gg/article/101090/Fort-Grey .