Fort Nelson had two entrances. The lower west one was flanked by the guard room with three cells and a stable for three officer's horses. This entrance gave access to the barrack block. It was defended by a minor branch of the ditch. A special lifting bridge called a Guthrie bridge was fitted to both entrances of each of the forts on Portsdown Hill. This withdrew into the fort after it had been lifted. The huge wooden gates of the fort are studded with metal to give greater protection.
The upper east entrance was over a long fixed bridge and guthrie lifting bridge. This entrance entered the fort at parade ground level.
Although an enemy was not expected to assault the fort from the rear, the redan was intended to be armed with 40pr R.B.L. guns on its upper floors. These guns could sweep the rear of the fort with case shot. Additionla guns could have been mounted in the redan to fire along the gorge ditches.