Landguard Fort has existed as a fortification since about 1500 but the surviving Fort largely dates from 1744. During the first half of the 19th Century little was done to update the fort but in 1871-76 the fort underwent major modifications that largely survive to this day. A defensible barracks was built in the interior, and the main face of the fort facing the river was provided with positions to mount four 9-inch RML guns. The work was subsequently extended to include seven casemates with iron shields, with five of these mounting 12.5-inch 38-ton RML guns, and the other two mounting 10.5-inch 18-ton RMLs. The outer wall was clad with granite. A large caponier was also built in the ditch below this new RML battery.
Landguard Fort had three external batteries:
A Submarine Mine Station was also built adjacent to the Fort, with a pier for deploying the sea mines.
The heavy RML Battery in Landguard Fort worked in conjunction with Shotley Point Battery and Beacon Hill Fort.