'Vengeance Weapon 3') was a German World War II large-caliber gun working on the multi-charge principle whereby secondary propellant charges are fired to add velocity to a projectile.

The Germans planned to use the weapon to bombard London from two large bunkers in the Pas-de-Calais region of northern France, but they were rendered unusable by Allied bombing raids before completion.

The V-3 was also known as the Hochdruckpumpe ("High Pressure Pump," HDP for short), which was a code name intended to hide the real purpose of the project.

In 1857, U.S. inventor Azel Storrs Lyman (1815–1885) was granted a patent on "Improvement in accelerating fire-arms",[8] and he built a prototype in 1860 which proved to be unsuccessful.

[24] France collapsed in June 1940 at the beginning of World War II, and German troops acquired the plans of this long-range gun.

Coenders thought that the gradual acceleration of the shell by a series of small charges spread over the length of the barrel might be the solution to the problem of designing very long range guns.

[9] The first tests were encouraging, but to get the support of the Ministry of arms, Hermann Röchling had to present to Albert Speer Coenders' project of a cannon capable of firing on London from the coast of the Pas-de-Calais.

After the Royal Air Force (RAF) bombed the Peenemünde rocket center on 17 August, Hitler agreed to Speer's suggestion that the gun be built without more tests.

Nonetheless, a proposal was made to build a single full-sized gun with a 150-metre (490 ft) barrel at Misdroy on the Baltic island of Wolin, near Peenemünde, while construction went ahead at the Mimoyecques site in France, which had already been attacked by the USAAF and the RAF.

The Heereswaffenamt (Weapon Procurement Office) took control of the project by March 1944, and, with no good news from Misdroy, Coenders became one of the engineers working on the three chief problems: projectile design, obturation, and ignition of the secondary charges.

[citation needed] The eastern complex consisted of five drifts angled at 50 degrees reaching 105 metres (344 ft) below the hilltop.

[33] The two guns were aimed west, resting on 13 steel support structures on solid wooden bases on a 34 degree slope.

The second gun tube was brought into operation on 11 January 1945 and 183 rounds in total were fired until 22 February 1945, with 44 confirmed hits in the urban area.

One gun was erected before the failure of the Nordwind offensive put the site at risk, and the equipment was removed before firing could begin.

There were other proposals to deploy batteries to bombard London, Paris, Antwerp and other cities, but they were not implemented due to the poor state of the German railway network and a lack of ammunition.

[31] The disassembled gun tubes, spare parts, and remaining ammunition were later captured by the US Army and shipped to the United States where they were tested and evaluated at the Aberdeen Proving Ground, Maryland, and scrapped there in 1948.

[33] The Mimoyecques museum allows visitors to view the galleries (in various stages of construction and bombing damage), remains of the guns, a small scale V-3 replica, and examples of machinery, rail systems and tools employed.

The site also contains memorials to the slave labourers who were forced by the Nazis to construct it[35] and to the airmen killed in action during the destruction of the base.

[36] Hugh Hunt of Cambridge University, together with explosives engineer Charlie Adcock, created a working scale model of the V-3 gun and was able to prove the ignition of the propellants was done by the advancing gas behind the projectile.