Garrison Point Fort is a two-tiered casemated fort similar to Fort Picklecombe in Plymouth. Garrison Point Fort was built between 1861 and 1872 over earlier fortifications including a blockhouse (1547), and bastion fort (1669). The Fort was intended to help protect the entrance to the Medway River and thus Chatham and Sheerness Dockyards. There was a boom defence across the Medway from Garrison Point Fort to Grain Tower. Grain Fort, Grain Wing Battery, Grain Tower and Grain Dummy Battery operated in conjunction with Garrison Point Fort to protect the entrance to the Medway and that stretch of the River Thames.
Garrison Point Fort was one of the Royal Commission Forts and was intended to be armed with two tiers of forty-four 9-inch and 10-inch RML guns behind iron shields. By 1880 the armament was shown as:
- Twenty-Eight 9-inch RML guns
- Ten 10-inch RML guns
- Three 11-inch RML guns
- Three 12.5-inch RML guns
By 1890 the RML guns had been supplemented by three 6-inch BL guns and four 12-pdr Q.F. guns. Most of the RML guns were still in place in 1898.
Between 1884 and 1907 a Brenan Torpedo was installed in Casemate 14 of the fort, primarily for training purposes.