The standard American grenade launching system in World War One was the Vivien-Bessiere, borrowed directly form the French. It had been adopted by France in 1916, replacing copies of the British Martin-Hale rod grenades. The V-B was a cup type launcher using a pass-through type of grenade and standard ball ammunition. A hole through the body of the grenade allowed the bullet to pass clean through the grenade, triggering a 5-7.5 second time fuse in the process. The gas pressure behind the bullet would then launch the grenade to a distance of 80-190 yards, depending on the inclination of the rifle. It could be fired from the hip if necessary, but firing form the shoulder was just a bad idea. The intended firing method was to rest the stock on the ground - although launching racks were also built for using the system from fixed positions in trenches.
The US would develop 4 iteration of the launcher, basically to improve its fixation to the rifle. This example is a Mk IV, with a spiral locking channel to firmly fix the launcher behind the rifle’s front sight. Two versions were made; a smooth one for the 1903 Springfield and one with a knurled ring at the muzzle for the 1917 Enfield. Both were identical in function, but dimensioned to fit the specific barrel diameters of the two different rifles. The Model 1917 V-B launcher would remain in US service until the 1930s, actually seeing some use in WWII in the Pacific theater.
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