rubble by rifled guns. The government's response was to appoint a Royal Commission on the Defence of the United Kingdom, which published a far-reaching report in 1860. The Royal Commission recommended that a triangle of forts should be established on the lower Thames, east of Gravesend. This would involve replacing the existing Coalhouse Fort on the Essex shore with a new fortification, similarly replacing the existing Shornemead Fort and building the wholly new Cliffe Fort opposite Coalhouse Point, which would replace the abandoned 18th-century battery at Lower Hope Point. The locations of the forts would enable interlocking arcs of fire from their guns. A boom defence and a minefield would be installed off Coalhouse Point in wartime to further boost the strength of the defences. The design of the new fort was similar to that of the other Royal Commission forts on the Thames, with an arc of granite-faced casemates, reinforced by iron shields. These, it was believed, would be virtually invulnerable to enemy fire. It was originally envisaged that the fort would have two tiers (in a design similar to that of Garrison Point Fort at Sheerness) mounting around 56 guns; 28 in casemates and the rest in barbettes on the fort's roof. Construction began on this basis in July 1861 but as the work progressed the design was changed, leaving the fort with only a single tier of casemates. Like its predecessors, its construction was seriously affected by the poor ground conditions and was disrupted by shifting and cracking foundations. Colonel Charles George Gordon, who was later to die in the siege of Khartoum, supervised its final phases of construction. The fort cost a total of £130,000 to build. Operational history 19th century It was originally intended that Coalhouse Fort would be armed with 68-pdr. smooth-bore guns, but these had become obsolete by the time it was completed in 1874. More powerful armour-piercing weapons were required, so the casemates were provided with four 12.5-inch and thirteen 11-inch RMLs with a range of about . A further three 9-inch RMLs were emplaced in the open battery. They were mounted on metal traversing platforms that could be elevated and traversed using hand-operated gearing devices. Operating the guns presented significant challenges; the 12.5-inch RMLs weighed up to apiece, used a charge weighing to fire a shell weighing to their maximum range, and broke windows half a mile away when they were