It owed its existence to the need to protect the important dockyards at Sheerness and Chatham from a perceived French naval threat during a period of tension in the 1850s.

At the time of the tower's construction, there were widespread fears that the imperial rivalry between Britain and France could result in a French invasion or naval incursion along the River Thames.

[2] The Medway also had major installations, notably the Chatham Dockyard, which had been targeted to devastating effect by the Dutch during the Second Anglo-Dutch War in 1667.

[1] Its location enabled the tower's arc of fire to overlap with that of the guns at Garrison Point on the Isle of Sheppey, on the other side of the Medway.

A fresh invasion scare at the end of the 1850s prompted the British government to appoint a Royal Commission on the Defence of the United Kingdom, which published a far-reaching report in 1860.

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

This required the construction of a raised concrete and stone structure on the tower's roof within which the new guns were emplaced, and a shelter was created to provide room for detachments, stores and fire control.

[3] The guns remained in place through the First World War, when the Grain Tower found an additional purpose as one end of a boom defence stretching across the Medway to Sheerness.

At the tower's rear, a brick and concrete barrack block standing on stilts was constructed to house the gun detachment.

[1] Grain Tower remains intact, though it is listed as "at risk" due to its poor condition and ongoing decay.

[11][12] The owner, a south-east London builder named Simon Cowper, said that "it just didn't work out well as a home – plus the cost of doing it [up].