- Official designation: fw3/27
- Shape: Octagonal
- Central Light Anti Aircraft or observation well
- Octagonal pillbox with sides of 11ft 7 inches (3.5m) with a porch on one side to protect the entrance
- Open well in centre is reached through double steel doors in the inner wall about 3ft (0.9m) above the ground and reached by iron rungs set into the wall.
- The central well is served either as a light anti-aircraft position or for observation.
- Often a timber post and pin would carry the LAA gun