was built around the edge of the common, used by military and naval officers. The construction of a railway line from London enabled the settlement of Southsea, named after the castle, to turn into a prosperous resort. Southsea Common was leased by the local government in 1884 and, as the population grew, practising firing the castle's guns became more difficult. 20th – 21st centuries At the start of the 20th century, Southsea Castle formed part of the "Fortress Portsmouth" plan for defending the Solent, the east battery equipped with two BL 6-inch (15.2 cm) Mark VII guns and two BL 9.2-inch (23.3 cm) Mark X guns, and the west battery armed with three 12-pounders (5.4 kg) and one 4.7-inch (11.9 cm) QF gun. During the First World War, the castle was at first manned by Royal Garrison Artillery and Number 4 company of the Hampshire Royal Garrison Artillery Territorials. Later these units were transferred to France and were replaced by the Hampshire Royal Garrison Artillery Volunteers. In response to the threat from German zeppelin raids, a QF 3-inch 20 cwt (10.9 cm 50.8 kg) anti-aircraft gun was added to the castle. Even though the castle remained in active military use after the conflict, by 1929 it had become a tourist attraction, and visitors were able to watch the castle garrison carry out practice firings out to sea. Southsea Common was bought by Portsmouth City Council in 1922 and turned into a park, while the west battery was disarmed in 1927. During the Second World War, the Hampshire Heavy Regiment, Royal Artillery (Territorial Army), occupied the castle, which was used as the Headquarters Portsmouth Fixed Defences. During the war, the castle was manned by a range of units including coastal artillery from the regular army and the home guard, and the east battery was armed with two 9.2-inch BL Mark X guns. Living conditions were poor, with the keep described by one member of the Auxiliary Territorial Service as "cold and wet and horrible". The castle was protected by barrage balloons, but it was hit by at least two incendiary bombs which did little damage. During the war, the castle was involved in an armed stand-off with French naval vessels. After the Fall of France in 1940, some of the French ships had made their way to British ports, including Portsmouth, but fears rose that the warships might leave and fall