holding 150 offenders under the supervision of a Royal Artillery sergeant who also oversaw the remaining artillery defences. The introduction of shell guns and steam ships in the 1840s created a new risk that the French might successfully attack along the south coast. In 1850, with the closure of the prison, seven 8-inch (22.3 cm) guns were mounted along the walls in brick emplacements, but there were concerns about the defences and two earthwork auxiliary batteries were built just alongside the castle to house additional guns. In 1856, at the end of the Crimean War, there was a large review of the fleet along the Solent, attended by Queen Victoria and numerous tourists. Naval gunboats launched a mock attack on the castle, which responded by firing a volley of forty 8-inch guns, causing chaos among the crowds watching around the base of the fortification. Fresh worries about France, combined with the development of rifled cannon and iron-clad warships, led to the Royal Commission on the Defence of the United Kingdom expressing fears about the security of Portsmouth in 1860. Lieutenant-Colonel Jervois oversaw the broader programme of work across the country, and was supported at Southsea by Lieutenant-Colonel Fisher. New gun batteries with underground magazines were constructed on the west and east sides of the castle between 1863 and 1869 to form part of a complex enclosed by a defensive wall; the old castle was used for range and direction finding, rather than to house weapons, and was left to slowly decline. By 1886, the site was well-armed, with 25 rifled, muzzle-loading guns and the design was praised by a visiting Russian military engineer. By the 1890s, the castle's defences had become obsolete once again due to the development of torpedo boats and superior breech-loading guns. In response, five 6-pounder quick-firing guns and searchlights were installed to deal with the torpedo boat threat and, between 1899 and 1901, the east battery was converted to hold breech-loading guns at a cost of £16,670. Meanwhile, in 1785, the government had taken possession of Southsea Common, the marshland surrounding the castle, to ensure it remained open and accessible to the fort's guns, and convicts were deployed to fill in and flatten out the marshes from 1831 onwards. The surrounding area began to develop as an urban centre; seaside facilities were established at the start of the century and in the 1840s new private housing