Beach Defence Post P4 includes not only a Lyon Light Emplacement but also a gun emplacement hacked out of the rock. Situated the small peninsular of Ras Il-Mignuna, it helps protect the Northern approaches to St Pauls Bay. Fort Campbell lies 600 metres to the north.
The pillbox had been modified but appears to have had two machine gun loopholes. There is central observation turret. The structure is concrete with a cladding of rocks for camouflage.
The Lyon Light emplacement is 15 metres immediately to the rear of the pillbox and linked by a path cut in the rock.
The gun emplacement is located adjacent to the pillbox with an elaborate covered entrance and expense lockers cut into the rock. There are no hold fasts but there is a T shaped grove cut in the rock, indicating it may have been for a Maxim Machine Gun.