Fort Nelson is a defensive fort located on Portsdown Hill, above Portsmouth, Hampshire.
The fort, built in the 1860's, is a Palmerston Fort. It is a six-sided structure, with a deep ditch protected by three caponiers. These caponiers allow defending soldiers to fire along the ditch, so the attacking force can not re-group in the ditch. Above the each of caponiers they built an emplacement for 13-inch mortars. These were originally entered by two Guthrie rolling bridges and had a barrack block for 172 men. These were protected by a V shaped redan.
Fort Nelson is one of five Portsdown Forts. These were built as a result of the 1859 Royal Commission by Lord Palmerston to prevent a land attack from the French on the Portsmouth dockyard. Although work was started on the fort in the early 1860's, it was not completed until the 1890's. The fort was disarmed in 1907 and then used for accommodation. In 1938 it was converted into an anti-aircraft ammunition store. The magazines were built on the parade ground. The fort was abandoned in the 1950's.
In 1988 the fort was set on fire by arsonists. This forced the MOD to reclaim the fort, but then they sold it to the Hampshire County Council for £50,000. The council restored the fort at a cost of £4 million. After the work was complete in 1994, they opened it to the public. In 1995 it became part of the Royal Armouries, housing their collection of artillery.
The fort is open all year round with no charge for entry. They hold live fire demonstrations every day.