fired. The detonations and clouds of choking black smoke generated when firing them presented a serious physical hazard to the gun crews. The guns were controlled from a Battery Commander's Post on the roof, from where commands to the gun detachments could be relayed via voice pipes. Three depression range finders were installed on the roof by the late 1890s to aid the guns' targeting. A well-trained crew could fire each gun once every two minutes. Rather than firing all the guns at once, the guns were positioned so that they could be fired in sequence as an enemy ship passed by. When combined with the fire from Shornemead and Cliffe Forts on the Kent shore, this would ensure that constant fire could be maintained from three different sides. The rapid development of artillery weapons in the late 19th century meant that the casemate style of fortification had become virtually obsolete within a decade of the fort's completion. Its original purpose of defending the river against large warships was taken over by a new East Tilbury Battery, constructed in 1891 about to the north-west just outside East Tilbury village. This contained six much more powerful breech-loading (BL) guns on Moncrieff disappearing carriages within concealed emplacements facing east up the river. A similar battery was built at Slough Fort on the Hoo Peninsula a few miles downriver. At the same time, a new threat had emerged in the shape of the fast and highly manoeuvrable torpedo boat. Large guns were virtually useless against such vessels, so the fort was supplemented with another new battery built in 1893 some to the south where 6-pdr. quick-firing guns were installed. Similar batteries were built on the opposite shore at Shornemead and Cliffe Forts. Early 20th century By the start of the 20th century the fort's casemates had been put out of use as they were too vulnerable to modern artillery. Instead, part of the fort's front was covered with a sloping glacis made of earth, blocking the casemates and filling the inner defensive ditch. At least one of the front caponiers was also demolished around this time. Most of the old RMLs were retired and replaced with four Mk. VII six-inch BL guns and four 12-pdr quick-firing (QF) BL guns, with ranges of and respectively, mounted on concrete emplacements on the fort's roof. The larger guns were intended to support those at East Tilbury