Like the LCF, the Landing Craft, Gun (Large) was a British conversion based on the LCT(3) or LCT(4). Two 4.7-inch guns, a type fitted to many destroyers, were placed on the decked-over tank deck. The craft was intended for bombarding enemy coastal defences at close range as the assault force landed. The LCG(L)(4) was given an improved bow for better seagoing ability, and armour one to two inches thick on vulnerable points.
Above: Line drawing of an LCG(L)(4), based on the hull of an LCT(4). (Image from: Baker, Rowland, ‘Notes on the Development of Landing Craft’ in, Duckworth, A.D. (ed.), Transactions of the Institution of Naval Architects, Vol. 89. (London: Institution of Naval Architects, 1947), pp.218-258.)
Nearly one-third of the Landing Craft, Gun (Large)s present at Normandy were operated by the US Navy rather than the British. Along with the LCFs, after D-Day these craft were used each night to form the Trout Line, a defensive line of landing craft on the eastern side of the landing beaches to protect the anchorage against nocturnal attacks by E-boats, human torpedoes and other German small craft.