Due to the excellent characteristics of the gun, it was decided to increase the weight of shell to 1,400 lb (635 kg), with an increased firing charge to achieve about the same range. The gun firing the lighter shell was designated Mark V(L) (for "light") by the
Royal Navy, and the 1,400 lb version Mark V(H) (for "heavy"). 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. They could be stored in railway tunnels when not in use to protect them from attack.
Experimental hypervelocity gun 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
Frederick Lindemann (Lord Cherwell),
Winston Churchill's scientific advisor. 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. 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. After further experimental firings, the weapon was taken out of service in February 1945. ==Service==