It was built during the American War of Independence to guard the Thames against French and Spanish raiders operating in support of the newly formed United States of America.

The interior of the fort - originally its parade ground - is occupied by a grass-covered lawn with flowerbeds, trees, ornamental bushes and a bandstand at the centre.

The northern sector, originally called the North Face,[2] contains two concrete semi-circular emplacements in which two 6" breech-loading guns were installed in 1904.

Sixteen storage rooms serving as expense magazines for cartridges and shells are situated off the tunnel, with ammunition lifts linking them to the gun positions above.

[4] The magazines have been partly refurbished with displays illustrating how they were used and exhibits relating to the military history of Gravesend, and are open as a visitor attraction on summer weekends.

[1] The lower Thames was of great strategic significance as the location of major military installations including the dockyard and arsenal at Woolwich, the powder magazine at Purfleet, and the victualling stores and shipyard at Deptford.

[5] The crossing between Gravesend and Tilbury was also of considerable importance, which had prompted the Tudors to build fortifications on both sides of the river at that point.

Serious weaknesses in British coastal defences had been revealed in 1778 by the American adventurer John Paul Jones in his raid on Whitehaven, Cumbria.

The state of the defences was found to be unacceptably deficient and plans were made for the building of 30 new batteries, positioned in an arc along the southern and eastern English coast from Norfolk to Cornwall.

With fears increasing of a French invasion in support of their American allies, the government approved Page's proposals and construction began soon afterwards.

[1] The rear of the fort was originally open,[10] but by the end of the 18th century a defence wall and caponier with loopholes for muskets had been built to close it off.

A new class of ironclad ships with powerful rifled muzzle loader (RML) guns, exemplified by the British HMS Warrior and the French La Gloire, posed a substantial threat to existing coastal defences.

[14] The existing magazines and ramparts were demolished and new brick emplacements were built, on which were mounted ten 9-inch and one 12-inch RML guns capable of ranges of up to 4,600 yards (4,200 m).

Advances in naval firepower meant that the principal line of defence for the Thames had been moved downriver to the batteries at Grain and Shoeburyness, where bigger guns with a longer range could control the entire estuary mouth.

[16] In 1905 the RML emplacements were replaced with two concrete pits for a pair of 6-inch breech-loading guns with a range of 6 miles (9.7 km), with separate magazines constructed to support them.

They were only emplaced for a few years and the fort was disarmed before the outbreak of the First World War in 1914 and was rearmed in 1930 with a pair of replacement 6-inch guns, used to train the Territorial Army's Gravesend battery.

A pair of 20-metre-high (66 ft) communications masts were built on top of the disused magazines to support a naval radio monitoring station.

[17] The Admiralty requisitioned the magazines in 1941 to utilise them and the connecting tunnels as air raid shelters for HMS Gordon, a naval shore establishment based in the nearby Sea School.

[1] Restoration got underway in 1975,[17] and in 1977 the fort was given a Grade II* listing for its architectural and historic interest, reflecting the unusual complete example that it presents.

[20] Two salvaged 6-inch guns were reinstalled in the fort in the 1980s, making it the only completely armed two-gun battery of its type in the UK mainland.