Two Redoubts were built on the hillside above Scala Battery. Together with a line of blockhouses they were intended to protect the perimeter of the whole Scala Battery. Crows Nest is composed of two position, adjacent to each other, built on top of large boulder. A smaller redoubt lay to the east which was shown as Eagles Nest (see TNA WO 78/5433). A crew shelter stands a short distance away.
At least eleven blockhouses were built around the perimeter of Scala and the Upper North Battery and Lower North Battery. These blockhouse are rudimentary, based on the experience during the Boer Wars.