21 cm K 12 ( E ) The 21 cm Kanone 12 in Eisenbahnlafette ( 21 cm K 12 ( E ) ) was a German railroad gun used in the Second World War . Design & History . Krupp continued theoretical research on a replacement for the Paris Gun during the Weimar Republic - era , but it was the Nazi government that finally authorized funding for experiments to solve some of its worst problems . The extremely high velocities used by the Paris Gun to attain the stratospheric heights necessary for extreme range caused enormous wear of the barrel . So much so that the shells had to be made in gradually increasing diameter to suit the rate of wear . Even then barrel life was merely 50 rounds . It is believed that the one Paris Gun destroyed by a premature detonation in the bore was caused by loading one of the serially - numbered shells out of order . Thus Krupp decided to use only 8 grooves in the barrel and to machine matching ribs or splines on the shells to obviate the need for a massive copper driving band to start the shell spinning without shearing off , which had been one of the prime causes of the excessive barrel wear in the earlier weapon . Gas sealing would be handled by a copper band , mounted in the place normally occupied by the driving band , with an asbestos and graphite packing to form the initial seal . A number of test barrels , known as the 10 . 5 cm K 12 M , and shells were made in 1935 and were compared to a conventionally rifled barrel ( the 10 . 5 cm K 12 MKu ) . The tests proved that Krupp ' s concept was correct . The K 12 ( E ) was mounted on a simple box - girder carriage , which was carried on two subframes which were in turn mounted on double bogies . The barrel was mounted in a ring cradle with a hydropneumatic recoil system . Two more hydropneumatic systems were connected to the subframes , which allowed the entire carriage to recoil some . For transport the gun itself was disconnected from its recoil system and drawn back some to reduce the mounting ' s overall length and allow it to fit in the normal railroad loading gauge . The barrel ' s extreme length required external bracing to prevent it from bending under its own weight . Its trunnions were placed as far forward as possible to balance the barrel and minimize the force necessary to elevate it . This placed the breech perilously close to the ground and a hydraulic jacking system was built in each subframe to elevate the mount . Unfortunately it was impossible to load the weapon in this position and it had to be lowered between every shot . The K 12 ( E ) could be fired from any curved section of track , a Vögele turntable , or from its special firing track . This prefabricated T - shaped track was carried on the gun train and deployed by a special crane wagon . Once the front bogies were at the crossover at the top of the T they were then jacked up and turned with the subframe 90° and then lowered onto the crosstroke of the T . The gun was then traversed by an electric motor to the bogies and it was clamped to the track once laid onto the target . It fired HE shells weighing . The first weapon was completed in 1938 and delivered to the Army Heer in March 1939 . It was successful , although the necessity to jack it up and down between shot wasn ' t well received by the Heer . Trying rectify this problem Krupp discovered that hydro - pneumatic balancing - presses could work at much greater weights and pressures than previously believed . They redesigned the mounting with the trunnions as far forward as possible and increased the recoil stroke to . The new design was delivered during the summer of 1940 and called the K 12 N ( E ) . The first gun was retrospectively called the K 12 V ( E ) . They spent the war assigned to Artillerie - Batterie 701 ( E ) along the Channel coast . The British recovered shell fragments near Chatham , Kent , some from the nearest point on the French coast .