Portland Castle was part of King Henry VIIIs plan for defending England from French invasion. The move was away from the classical huge scale castles and towards strings of defendable positions which were strategically placed to create crossfires and killing fields. The castle at Portland was built during the mid-1500’s to create a crossfire with castles in Weymouth across the harbour.
Like many defences, Portland Castle was built to repel a French invasion which never came. The structures use for storage during both World Wars means that it only ever saw real action duringt the English Civil War of the 1600’s where it was captured by the Parliamentary forces.