The V3 Supergun,
The third installment of Hitler’s vengeance weapons, (the first being the V1 and V2 rockets), the V3 was a large supergun created by the Germans during World War II. At 140 meters long, it could deliver a 140kg (308lb) shell over 165km (102.5 miles). The most unique feature of the gun was that it used multiple charges placed throughout the barrel to help propel the projectile. As the projectile passed through the barrel timed charges would ignite propelling the projectile faster and faster until it left the bore.
While an ingenious design, the V3 cannon were not very practical, mostly because, once constructed they could not be moved without disassembling the entire gun. As a result, the gun could also only fire in one direction. Hitler ordered the construction of 50 such guns all over France, but few were made due to Allied bombing. Two guns were created in northern France to bombard London, but were destroyed by Allied bombers before they could be used. In December of 1944 two guns were secretly built and used to bombard Luxembourg, which was then under Allied control. The bombing lasted until February of 1945, but led to only a few dozen casualties, causing insignificant damage to an army numbering in the hundreds of thousands. The guns were captured at the end of the war and destroyed with dynamite.