Fort Cumberland is a pentagonal artillery fortification erected to guard the entrance to Langstone Harbour, east of the Dockyard of Portsmouth on the south coast of England.

It was sited to protect the Royal Navy Dockyard, by preventing enemy forces from landing in Langstone Harbour and attacking from the landward side.

Within the body of the fort, a number of brick buildings were constructed, comprising a guardhouse, storeroom and powder magazine; of the two proposed barrack blocks, only one is believed to have been completed.

Fort Cumberland was completely rebuilt in masonry, and on a considerably larger scale, as part of a programme to improve the fortifications of Portsmouth.

In the course of construction all traces of the original fort were destroyed, with the exception of the guard house and store room, both of which were incorporated into the new design.

By the late 1850s, the development of rifled cannon had rendered the fort's smooth bored muzzle loading ordnance obsolete.

[3][4] The fort saw brief action during the Second World War when, on 26 August 1940, it was hit by a German air raid in which eight Royal Marines were killed, amongst them Second Lieutenant Harold Jameson.