It was repeatedly altered and its guns upgraded at various points in its history, before being decommissioned in 1956 when the UK abolished its coastal defence programme.

Britain's coastal defences had not been substantially upgraded since the Napoleonic Wars, but a new generation of accurate and powerful guns, mounted on fast-moving, manoeuvrable iron-clad warships, had obsoleted the existing 18th and early 19th century forts along the British coastline.

[1] The government's response to the increased threat was to appoint a Royal Commission on the Defence of the United Kingdom, which published a far-reaching report in 1860.

It had been built in the style of a Martello tower between 1848 and 1855 but the introduction of powerful and accurate rifled muzzle loader (RML) guns during the 1850s made it obsolete as soon as it was completed.

[3] The 1860 Commission report recommended that Grain Tower should be turned into a fully casemated fort, which would be built around the existing structure.

It provided barrack accommodation for the garrison and was designed to be defensible, with loopholes in its front face to facilitate musket fire.

Similarly, its gorge at the rear, where the main entrance stood, had crenelations to provide protection for defenders faced with a rearward attack.

The fort continued in use during the Second World War and underwent further alterations when its two existing 6-inch close defence guns were enclosed within bomb-proof shelters.

The fort's earthworks and a brick revetment still survive and a path links the concrete aprons of the infilled gun emplacements.