Battery while the smaller ones provided a defence against fast-moving vessels such as destroyers and torpedo boats. Despite their obsolescence, two of the old 12.5-inch RMLs remained at the fort until as late as 1912. They were to be used as "giant blunderbusses" to spray torpedo boats with grapeshot if they got past the other guns. Coalhouse Fort was manned during the First World War by No. 2 Company, Royal Garrison Artillery, which manned the guns; the 2nd Company London Electrical Engineers operated the electric searchlights. A minefield was installed in the river between Shornemead and Coalhouse forts, with mechanically operated mines in the shallower parts of the river and remotely detonated mines in the navigable channel. Friendly ships could thus pass freely but the mines could be detonated by a shore-based observer if an enemy ship tried to use the main channel. Coalhouse Fort took on the role of an Examination Battery controlling the river traffic in conjunction with the River Examination Service. Incoming vessels were checked by tugs based alongside the old HMS Champion, moored in midriver, and if any vessel was deemed suspect or refused to stop, the fort was authorised to fire across its bows. The fort's armament was reduced during the war as other forts and batteries took over some of its duties. Two of the six-inch guns were shipped across the river to Cliffe Fort in 1914 and the QF guns on the roof were withdrawn. An anti-aircraft battery was established north-west of the fort for defence against Zeppelins and enemy bombers. 1920s to 1940s Following the end of the war, it was proposed in 1924 that Coalhouse Fort should be re-equipped with 4-inch guns but post-war defence cuts meant that this plan was abandoned. Instead, the fort was reduced to care and maintenance status and East Tilbury Battery was decommissioned in 1930. The continuing development of artillery firepower meant that the forts and batteries further downriver took on an increased responsibility for the forward defences of the Thames. The forts on Gravesend Reach were relegated to a second line of defence. Coalhouse Fort became an "emergency" battery during the anti-invasion preparations of the early Second World War. The existing 6-inch guns were replaced in July 1941 with two 5.5-inch guns which had been removed from HMS Hood during a refit in April 1940. These had a range of and were installed in two