Fort Amherst is now open as a visitor attraction throughout the year with tours provided through the tunnel complex The primary purpose of all the Medway fortifications was the defence of the Naval Dockyard.

This was largely the result of the Raid on the Medway in 1667 when the Dutch fleet inflicted heavy damages on the dockyard.

The first plan of defences was an enceinte (ring of fortifications), from Gun Wharf, Chatham, to north of the village of Brompton.

[9] Also in 1802–11, prisoners, mostly convicts from St Mary's Island,[7] were set to work on extending the tunnels and creating vast underground stores and shelters, new magazines, barracks, gun batteries and guardrooms.

A second gun battery, 'Townsend Redoubt', was built at the northeastern corner of the dockyard at the same time as Fort Amherst.

Both forts were inside the 1756 brick-lined earthwork bastions known as the "Cumberland Lines", which surrounded the whole east side of the dockyard down to St Mary's Island.

The entire fortified area was then used as a training-ground during the Victorian era, with practice sieges becoming so popular that they attracted thousands of visitors to Chatham.

[10] Fort Amherst has been described by English Heritage as the most complete Napoleonic fortification in Britain and as such has great national historical significance.

[3] In the late 1970s a group of enthusiasts were given permission by the Ministry of Defence to start tidying up the site, with the intention of restoring the fort.

The trust have also run a programme of regular events, including ghost tours, which typically take place on the first Friday evening of each month, and over-night paranormal investigations through the tunnels.

The bridge leads to a part of the fort also known as Spur Battery and to the Inner Lines - the Napoleonic defensive ditches.