The origin of the multi-chamber gun dates back to the 19th century. In 1857, U.S. arms expert Azel Storrs Lyman (1815–1885) was granted a patent on "Improvement in accelerating fire-arms", and he built a prototype in 1860 which proved to be unsuccessful.Lyman then modified the design in collaboration with James Richard Haskell, who had been working for years on the same principle.
Haskell and Lyman reasoned that subsidiary propellant charges could increase the muzzle velocity of a projectile if the charges were spaced at intervals along the barrel of a gun in side chambers and ignited an instant after a shell had passed them. The "Lyman-Haskell multi-charge gun" was constructed on the instructions of the U.S. Army's Chief of Ordnance, but it did not resemble a conventional artillery piece. The barrel was so long that it had to be placed on an inclined ramp, and it had pairs of chambers angled back at 45 degrees discharging into it. It was test fired at the Frankford Arsenal at Philadelphia in 1880 and was unsuccessful. The flash from the original propellant charge bypassed the projectile due to faulty obturation and prematurely ignited the subsidiary charges before the shell passed them, slowing the shell down. The best velocity that could be obtained from it was 335 metres per second (1,100 ft/s), inferior to the performance of a conventional RBL 7 inch Armstrong gun of the same period. New prototypes of multi-charge guns were built and tested, but Lyman and Haskell abandoned the idea.A suitable site was selected at a limestone hill about 5 kilometres (3.1 mi) north of the Hidrequent quarries, near Mimoyecques in the Pas-de-Calais region of northern France behind Cap Gris Nez, very close to the French end of the present day Channel tunnel, where V-1 and V-2 launch sites were already under construction. The site was 8 kilometres (5.0 mi) from the sea and 165 kilometres (103 mi) from London. It was code-named Wiese (meadow) and Bauvorhaben 711 (Construction Project 711), and Organisation Todt began construction in September 1943 with the building of railway lines to support the work, and began to excavate the gun shafts in October. The initial layout comprised two parallel facilities approximately 1,000 metres (3,300 ft) apart, each with five drifts which were to hold a stacked cluster of five HDP gun tubes, for a total of 50 guns. Both facilities were served by an underground railway tunnel and underground ammunition storage galleries.There were other proposals to deploy batteries to bombard London, Paris, Antwerp and other cities but these were not implemented due to the poor state of the German railway network and a lack of ammunition.
http://secretweaponsoftheiiireich.blogspot.com/2011/08/v3-england-canon.htmlwww.youtube.com/watch?v=69Bcce-ogQQ
