All the major belligerents in World War I save one were party to the Hague Convention of 1899, whose signers had agreed “to abstain from the use of all projectiles the sole object of which is the diffusion of asphyxiating or deleterious gases.” The exception was the United States. The idea of outlawing poisonous weapons dated back to the American Civil War, but Alfred Mahan, the naval theorist and an American delegate at the Hague conference, explained that no such chemical artillery had yet been developed and that “until we knew the effects of such asphyxiating shells, there was no saying whether they would be more or less merciful than missiles now permitted.” Mahan added that
it was illogical, and not demonstrably humane, to be tender about asphyxiating men with gas, when all were prepared to admit that it was allowable to blow the bottom out of an ironclad at midnight, throwing four or five hundred into the sea, to be choked by water, with scarcely the remotest chance of escape.1
However, the concerns of the European nations went beyond considerations of tenderness to troops in the field. The emergence of the European chemical industry in the second half of the nineteenth century, especially in Germany, had given rise to fears that lethal gases could be produced as weapons that, if used on the battlefield, would drift with the winds, jeopardizing civilians. They were thus outlawed in advance of being produced.
The first significant gas attack of the war, launched by the Germans at Ypres on April 22, 1915, kept to the letter of the convention, if not its spirit, by releasing chlorine gas from 5,730 cylinders fixed in place, rather than from projectiles. The chlorine formed a thick green-yellow cloud about five feet in height that wafted westward on a breeze toward the Allied trenches and gradually grew to a height of about thirty feet. Soon hundreds of men were choking and vomiting and dying while the rest of the troops fled in panic to the rear. A German officer recalled of the gas attack:
…The commission for poisoning the enemy, just as one poisons rats, struck me as it must any straightforward soldier: it was repulsive to me. If, however, the poison gas were to result in the fall of Ypres, we would win a victory that might decide the entire campaign. In view of this worthy goal, all personal reservations had to be silent. So onward, do what must be done! War is necessity and knows no exceptions.
Following such logic, the Allies established chemical warfare programs, and so did the United States, which consolidated its various new chemical weapons efforts in May 1918 into an Army Chemical Warfare Service. By then, both sides had abandoned the legal nicety of the mode of attack used at Ypres and were firing artillery shells filled with different gases, including phosgene, which was eighteen times more toxic than chlorine, and mustard agent, an oily…
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