Horsea Island

Horsea falls within the city of Portsmouth and was wholly owned by the Ministry of Defence as part of the shore establishment HMS Excellent, which maintains its headquarters on Whale Island.

In 1804 a Royal Powder Works was established on Little Horsea in connection with the gunpowder magazine at nearby Tipner; by 1849, however, it was no longer in operation, and no above-ground evidence of the site remains to be seen.

[2] The islands were joined to form a torpedo testing lake in 1889, using chalk excavated from Portsdown Hill, 1 km to the north, by convict labour.

After closure of the telegraphy station in the 1960s, the northern part of the island became home to HMS Phoenix, the naval school of firefighting and damage control.

Where still exposed, beyond the lake at the eastern end of the site, the brickearth comprises fairly equal proportions of sand, silt, and clay, with occasional flints.

The lake contains a wealth of marine life, and also holds a number of items placed for diver training, including a helicopter, vehicles, and a 200-year-old shipwreck placed in the central section.

All of the undeveloped area to the southwest of the lake, with the exception of the helipad, forms one of the few terrestrial parts of the Portsmouth Harbour Site of Special Scientific Interest (SSSI) on account of its calcicole flora and fauna[5] which have flourished on the imported chalk.

Notable fauna includes the small heath butterfly Coenonympha pamphilus, designated BAP Priority Species by DEFRA on account of its increasing scarcity.