So much for the substance which outdid any of the horrors of the most horrible of all wars. But the weapon was useless unless protection against it could also be developed. America invented the protection--thick felt which was a textile triumph in that it absolutely caught and held the smoke particles, yet permitted fairly easy breathing through itself. The plan was to issue this felt in small pieces which the soldiers could wrap around their canisters, in order that all inhalation should be through the felt. The felt-wrapped canister would then be placed back in its knapsack. In the joint project, we were to produce the protective felt and the British the candles. The British had ordered several million of these and were actually producing them in large quantities at the time of the armistice. By that date the American mills were turning out the felt by thousands of yards, and our Chemical Warfare Service was also planning a factory in which to produce diphenolchlorarsine candles. All this activity was an intense secret in both countries. The program was being directed at a certain week in the spring of 1919, when, at a favorable hour, the troops on our side having quietly been protected against the smoke, it was proposed to fire the candles everywhere along the front. The gas warfare organizations of Great Britain and America confidently expected that when that lethal infusion had disappeared, the German Army would practically have ceased to exist, and the war would be over. There is reason to believe that the German also realized the inefficiency of diphenolchlorarsine when fired in shell and had followed an independent line of development which led him to the production of candles. It is asserted that such candles were made in Germany before the armistice. It is doubtful, however, whether the German succeeded in developing a protection against the smoke. After the armistice our Chemical Warfare Service continued an independent development of arsenical smoke. The problem was a mechanical one. The chemical is driven off as smoke by means of heat. If the heat is too great, the substance will burn and be changed into non-toxic compounds. If the heat is too mild, the smoke will not be thrown off efficiently. This problem we have solved.