Rerrin Infantry Redoubt was built approximately 150 metres to the South West of Rerrin Battery on Bere Island. The Redoubt was intended to protect the flank of the battery from land attack as well as deny this high ground, within rifle range of Rerrin Battery, from enemy occupation.
Plans for the infantry redoubt were not drawn up until 1902, about the time work was nearing completion on Rerrin Battery. The Redoubt was not completed until 1907. The redoubt remains largely complete, although with some modification.
The main command post for Bere Island East Fire Command was positioned on the south face of the Rerrin Redoubt. Here there is a Position Finding Cell and underground fire control room. The redoubt was to be manned by infantry supported by machine guns.