Then there were the special weapons, largely born of modern trench warfare. These included mortars, ranging from the small 3-inch Stokes, light enough to go over the top and simple enough to be fired from between the steadying knees of a squatting soldier, to the great 240-millimeter trench mortar of fixed position. The mortars proved to be exceedingly effective against concentrations of troops, and so there was devised for them a great variety of bombs and shell, not only of the high explosive fragmentation type, but also containing poison gas or fuming chemicals. Great quantities both of mortars and their ammunition were required. From the security of the trenches the soldiers first threw out grenades, which burst in the enemy's trenches opposite and created havoc. From the original device were developed grenades of various sorts--gas grenades for cleaning up dugouts, molten-metal grenades for fusing the firing mechanisms of captured enemy cannon and machine guns, paper grenades to kill by concussion. Then there were the rifle grenades, each to be fitted on the muzzle of a rifle and hurled by the lift of gases following the bullet, which passed neatly through the hole provided for it. The production of grenades was no small part of the American ordnance problem. In addition to these trench weapons were the Livens projectors, which, fired in multiple by electricity, hurled a veritable cloud of gas containers into a selected area of enemy terrain, usually with great demoralization of his forces. Bayonets for the rifles, bolos, helmets, periscopes for looking safely over the edges of the trenches, panoramic sights, range finders--these are only a few of the ordnance accessories of general application. Then those innovations of the great war--the tanks--the 3-ton "whippet," built to escort the infantry waves, the 6-ton tanks, most used of all, and the powerful Anglo-American heavy tanks, each mounting a 37-millimeter cannon and four machine guns.