In the late 19th century a sea battery was added to give a wide field of fire to the south. Access is through the ground floor vault to the right of the courtyard. The sea battery consists of a central triangular block with five gunports almost at sea level, equipped with shutters to protect the guns from the elements. Today only the iron frames that held the shutters remain. Rifle slits protect the landward entrance to the battery. There are also two bastions to the west and east with a gate giving access to the shore. The whole battery had a proper parapet but only the three gun embrasures at the eastern end survive.