BL 13.5-inch Mk V naval gun

In 1939 three WW1 BL 14 inch Railway Guns (named Gladiator, Piece Maker and Scene Shifter) were removed from storage at RAOC Chilwell and recommissioned. The original 14" gun barrels had long since been scrapped, so they were fitted with BL 13.5 inch /45 Mark V gun barrels from the Royal Navy's Duke class reserves, which had been designed close enough to the dimensions of the 14" barrels to fit.[2] In 1940 these guns were issued to the Royal Marine Siege Regiment at Dover in Kent to bombard German batteries and shipping in the Calais area.[3] They could be stored in railway tunnels when not in use to protect them from attack.

A 13.5/8 inch hypervelocity gun (a type of very large-calibre artillery) for stratospheric experiments was developed and deployed near St Margaret's in Kent. The weapon was a 13.5 inch gun Mark V lined down to 8 inches; the liner projected several feet beyond the 13.5 inch barrel. The concept was suggested by F. A. Lindemann, Winston Churchill's scientific advisor.[4] Due to its deployment near the heavy cross-Channel guns and manning by the Royal Marine Siege Regiment, it is often erroneously assumed to have been intended as a cross-Channel gun. It was initially named Wilfred, but this was soon changed to Bruce, after Admiral Sir Bruce Fraser.[5] The projectiles were custom-made with external rifling to match the gun's rifling, with tighter tolerances than normal; this resulted in the need for a screwdriver-type tool to ram the projectiles. The rate of fire was very low as a result; but this was not a major concern in an experimental piece. Both high explosive and high velocity shells were made for the gun; the high velocity shell was a smoke shell, intended to burst at high altitude. Observations of the smoke were used to study conditions in the stratosphere. The gun was first test-fired in June 1942 at the Isle of Grain, also in Kent.[5] The gun was deployed near St. Margaret's on 21 January 1943, and experimental firing commenced on 30 March 1943. Successful experiments with smoke shells were conducted in February 1944. The intended burst zone for the smoke shells was 30 miles (48 km) horizontally from the gun and at 95,000 feet (29,000 m) altitude. These trials resulted in the need for a new barrel or liner; the replacement took about two weeks.[5] The data from these experiments was important in the development of the Grand Slam bomb.[6] After further experimental firings, the weapon was taken out of service in February 1945.[5]

• 340mm/45 Modèle 1912 gun French equivalent