Nordenfelt sold guns and ammunition for the 57 x 224 cased round to both Belgium and Russia, along with permission to build their own guns and mfg their own ammunition. When the Germans blew through Belgium in 1914, they captured many of these guns and great stores of ammunition. This was an older design, drop breech block with no recoil system, used primarily as a Fortress mounted gun or on a field carriage as a flanking gun using canister. The Germans used the guns for a couple of years but in 1916 decided to rebuild them. Photos are scarce of the rebuilt gun, but the one I saw showed two recoil cylinders on top of the barrel and a shield in front of the gun, and it was mounted on the back of a flat bed truck. It was to be used as a mobile anti-tank gun. At the same time the guns were being modernized, High explosive and anti-tank ammunition was being developed, also an optical sight. The German head stamped cases are from 1916-18, a nose fuzed HE and an internal fuzed APHE were designed. The older Belgian, Nordenfelt and Russian ammunition was low explosive black powder filled. With the new HE ammunition, optical sight and now rebuilt quick firing gun, targets could be engaged and destroyed at up to 2000 meters. The APHE round uses the Naval design with a hardened nose piece with a flat tip and an internal fuze with slight delay. The HE shell used a fuze unique to this round, both designs are in the British Notes on German Shells. When the A7V tank was being developed, the early choices for main gun were two of the 20mm Becker auto gun, the Gruson 53mm and the Krupp Fk96n/A field gun. The Beckers were found to be too erratic in function and too low in destructive power, the 53mm Gruson was too old a design, the FK96 77mm gun was just too big and heavy and with nearly a 36 inch recoil would be too unwieldy in the confines of the tank. The rebuilt 57mm Nordenfelt gun was perfect, had only a 6 inch recoil which left plenty of room behind the gun for a huge box of ammunition, and it was already rebuilt and being used. One of the problems encountered at this late date of the war was the inability to get enough of the optical sight, so some of the tanks had a larger cutout for the gun and just fired over open sights. The gun was also used in captured British tanks, replacing the Hotchkiss guns with the new Nordenfelts. A second batch of these guns came out of Russia so the Germans had plenty to work with. Interesting that the Germans did not just manufacture their own ammunition for the captured British tanks. They apparently thought their new model Nordenfelt was so superior that they went through the trouble to replace them in the British tanks..............