When the movements of armies in the great war ceased and they were held in deadlock in the trenches, the fighters at once began devising weapons with which they could kill each other from below ground. For this purpose they borrowed from the experience of man running back to time immemorial. They took a leaf from the book of the Roman fire-ball throwers and developed the hand grenade beyond the point to which it had been brought in the European warfare of the last century. They called upon an industry which had once existed solely for the amusement of the people, the fireworks industry, for its golden rain and rainbow-hued stars for signals with which to talk to each other by night. Other geniuses of the trenches took empty cannon cartridges and, setting them up as ground mortars, succeeded in throwing bombs from them across No Man's Land into the enemy ranks. They even for a time resurrected the catapult of Trojan days, although this device attained no great success. But from all such activities new weapons of warfare sprang, crude at first, but later refined as only modern science and manufacture could perfect them. America entered the war when this development of ordnance novelties had reached an advanced state. It became necessary for us, then, to make a rapid study of what had been done and then go ahead with our own production either from foreign designs or with inventions of our own. To this end in April, 1917, a few days after we declared war with Germany, the Trench Warfare Section was organized within the Ordnance Department and given charge of the production of these novelties. The section did not entirely confine itself to trench-warfare materials, since one of its chief production activities was concerned with the manufacture of the various sorts of bombs to be dropped from airplanes. Also, at the start of its existence it had charge of the production of implements for fighting with poison gas and flame. Although in large part this phase of its work was taken away from it in the summer of 1917 and was later placed under the jurisdiction of the newly organized Chemical Warfare Service, the Trench Warfare Section continued to conduct certain branches of gas-warfare manufacture, in particular the production of the famous Livens projectors of gas and also the manufacture of the portable toxic-gas sets for producing gas clouds from cylinders. All in all, the Trench Warfare Section was charged with the responsibility of producing some 47 devices, every one of them new to American manufacture and some extremely difficult to make. The backbone of the program consisted of the production of grenades, both of the hand-thrown and the rifle-fired variety, trench mortars, trench-mortar ammunition, pyrotechnics of various sorts, and bombs for the airplanes, with their sighting and release mechanisms.