of the old 6-inch emplacements. A steel shelter was constructed on the fort's roof to protect the guns, which were also camouflaged with netting. A brick observation post on the roof provided range-finding, and two remotely controlled searchlights installed on the roof of the north caponier could illuminate the riverside below. The purpose of these installations was to protect against raids by cruisers and torpedo boats and to counter any landings in the Thames. The fort's defences were also enhanced with two light anti-aircraft guns, including a Bofors 40 mm gun installed on the roof in August 1943, while the fort's perimeter was surrounded by barbed wire and trenches. Two spigot mortars were installed at the fort's rear; their bases can still be seen today. A detached concrete observation tower was built just north of the fort for use as an Extended Defence Officer's Post, to control the electrically detonated mines that had been laid in the river. A radar tower manned by naval personnel was also built south of the fort by 1941 to cover the approaches to the minefield, and an anti-aircraft battery was built to the north-west at Bowaters Farm in August 1939. It was frequently used in defence of the eastern approaches to London and was bombed on more than one occasion. By 1944 the threat of invasion had abated and the fort was handed over to the Home Guard's No. 356 Coast Battery detachment. Its complement at this time was a captain, two lieutenants and 103 other ranks. They were supplemented by a detachment of Wrens who operated a degaussing range established at Coalhouse Fort in 1943 under the name of HMS St Clement. Outbound ships passed over submerged sensors which detected whether the steel in their hulls had been demagnetised to a sufficient extent to make them undetectable by German magnetic mines. If they were detected, they would be recalled for further degaussing. As one of the Wrens later recalled, they found themselves "surrounded by a wonderful array of young men, soldiers and marines of all ranks – and we were the only girls in sight." HMS St Clement became a Combined Operations base and evolved into HMS St Clement I, II and III. As HMS St Clement III, the fort's last military designation, it was used after 1946 by the Admiralty for training Sea Cadets and nautical youth groups. It was decommissioned in