Support Defence Post L17 is a single storey pillbox of concrete with stone cladding. There is a single heavy machine gun loophole facing south down the main road. The Post has a triangular shaped concrete shelter on the roof and it would appear that this was used for a light crew weapons, such as a Bren Gun or Boys Anti Tank rifle.
There is a similar structure, on its own, situated adjacent to Support Defence Post L48 near Fort Leonardo.