Squadron. Sandown Castle in Kent, suffering badly from coastal erosion, began to be demolished from 1863 onwards; Hull Citadel and its 16th-century fortifications were demolished in 1864 to make way for docks; Yarmouth was decommissioned in 1885, becoming a coastguard signalling station; and Sandgate, also suffering from coastal erosion, was sold off to the South Eastern Railway company in 1888. 20th–21st centuries 1900–1945 By the start of the 20th century, developments in guns and armour had made most of the Device Forts that remained in service too small to be useful. Modern weapons systems and their supporting logistics facilities such as munitions stores could not fit within the 16th-century designs. A 1905 review of the Falmouth defences concluded that the naval artillery at St Mawes had become superfluous, as the necessary guns could be mounted at combination of Pendennis and newer sites along the coast, and the castle was disarmed. A review in 1913 concluded that keeping naval artillery at Calshot was also unnecessary, and the site was turned into an experimental seaplane station instead. Meanwhile, concerns had been growing about the unsympathetic treatment of historic military buildings by the War Office; for its part, the War Office was concerned that it might find itself financially supporting these properties from its own budget. Yarmouth Castle was passed to the Commissioners of Woods and Forests in 1901, with parts of it were leased to the neighbouring hotel. The War Office concluded that Walmer and Deal had no remaining military value and agreed to transfer the castles to the Office of Works in 1904, who opened both former fortifications to visitors. Portland Castle was placed onto what was known as the Schedule C list, which meant that the Army would continue to use and manage the historic property, but would receive advice on the suitability of repairs from the Office of Works. With the outbreak of the First World War, naval operations were mainly focused along the south-east and southern coasts. The defences of Pendennis were reinforced, while Southsea, with the addition of anti-Zeppelin guns, formed part of the Fortress Portsmouth plan for defending the Solent. Calshot formed a base for anti-submarine warfare, and the remaining castles of the Downs were used to support the activities of the Dover Patrol. St Mawes and Portland were used as barracks, and Walmer became a weekend retreat for the Prime Minister, Asquith, exploiting its good