Grain Tower Battery was constructed between 1879 and 1855 of granite in an Martello tower style. Unique by virtue that it was constructed off shore on a mud-spit in the River Medway, and only accessible by foot along a (muddy) brick causeway at low tide. The fort was initially armed with a 56lb gun and a pair of 32lb canon. Fifty five years after construction (1910 – 1912), the fort was upgraded prior to the outbreak of WW1 to accommodate two 4.7″ QF guns. The next upgrade came in 1940 when the two storey barrack block was constructed along with the Battery Observation Post and a twin 6lb Quick Firing (QF) gun. The Battery has been listed since 1986 under the Planning (Listed Buildings and Conservation Areas) Act 1990 for its special architectural and historic interest.