Fort Grey, Historic fort in Saint Peter's, Guernsey.

Fort Grey stands as a white-painted Martello tower on a tidal islet in Rocquaine Bay, connected to the mainland by a raised causeway and featuring granite construction with distinctive sloping walls characteristic of early 19th-century coastal defense architecture.

A small fort, probably built in the Late Middle Ages, stood on the rock and was used by the militia in the 1620s but was unfit to withstand an assault. The present white tower was built in 1804 during the Napoleonic Wars by local builder Thomas Henry of Clos du Valle and named after Charles Grey, 1st Earl Grey, Governor of Guernsey 1797–1807. The War Office sold it to the States of Guernsey in 1891 for £185; under German occupation in World War II it was renamed Widerstandsnest Grauer Turm and armed with a 3.7 cm Pak 36 and machine guns.

The rock beneath the tower is the Château de Rocquaine, in Guernésiais Châté dé Rocquoïne. In the 16th century it was said to host local witches' sabbaths; in 1617 a local girl, Isabel Becquet, was reported to have met the devil there, and Marie de Callais of St Martin was convicted of belonging to the coven and burnt at the stake on 17 October 1617.

Fort Grey is reached by a slipway from Rocquaine Bay that is covered at high tide, so time a visit for low water. The tower now holds a shipwreck museum with salvage from the MV Prosperity and Elwood Mead, and a cannon from HMS Boreas aimed toward the Hanois rocks. The fort and its slipway were listed as a Protected Monument (PM238) on 26 March 1938.

The War Office sold Fort Grey to the States of Guernsey in 1891 for £185. During the German occupation it was renamed Widerstandsnest Grauer Turm and armed with a mobile 3.7 cm Pak 36 anti-tank gun and machine guns. The museum's cannon from HMS Boreas points toward the Hanois rocks, where Boreas sank in 1807 with her captain and at least half the crew.