Fort Horsted was originally recommend by the Royal Commission on the Defence of United Kingdom in 1860 as part of the land defence line to protect Chatham Dockyards. Actual construction of the Fort did not commence until 1880 and was to last for nearly a decade. By the time that the fort was completed it was largely redundant, and it was never armed with any ordinance.
The forward casemates in Fort Horsted had positions to mount field artillery and there were six serving rooms on the this level with lifts down to the expense magazines. The magazine level included casemates for accommodation and access to steep three tunnels leading to the Left, Right and Central counter-scarp galleries.
The fort was used as an ammunition depot and mounted a 3.7-inch Battery and three Bofors 40mm guns. The Bofors positions survive as do two pillboxes from the same period.