Discharge of a huge French cannon caught by the camera just as the projectile left for the German lines. The gunners have stuffed their fingers into their ears to protect them from noise of explosion. Underwood and Underwood, circa 1918. The French 75 mm field gun was a quick-firing field artillery piece adopted. It was the first field gun to include a hydro-pneumatic recoil mechanism, which kept the gun's trail and wheels perfectly still during the firing sequence. Since it did not need to be re-aimed after each shot, the crew could fire as soon as the barrel returned to its resting position. At the opening of World War I, in 1914, the French Army had about 4,000 of these field guns in service. By the end of the war about 12,000 had been produced.