Why We Didn’t Use Poison Gas in World War II

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Untroubled by his defeat on the A-bomb, Marshall continued to argue against FDR’s pledge not to use gas. He soon found an ally in Gen. Douglas MacArthur, commander in the Pacific, who could see “no reason why we should not use gas right now against Japan proper. Any kind of gas.” Unlike Marshall, MacArthur was not hesitant about killing civilians or using the most poisonous gases.

Marshall also received important support for gas warfare from Assistant Secretary of War John J. McCloy, who argued for reconsidering policy “in the face of the public pressure for the use of gas, which may develop as our casualties rise due to the Okinawa cave type of Japanese defense.” McCloy, a distinguished Wall Street attorney, seemed perfectly comfortable about redefining the ethics of war. In the crucible of World War II, morality had been substantially altered; saving American lives and insulating the military from public criticism were McCloy’s main concerns.

At Marshall’s behest the Army’s Operations Division (OPD) in early June put together a paper offering both new and familiar rationales for using gas in the Pacific: It would save American lives, and the British no longer feared German retaliation. There was, however, a serious danger that Japan would retaliate against noncombatant populations, especially in China and in Manchuria and Korea, although such retaliation would be “only to a limited extent.” And the OPD acknowledged that the introduction of gas would erode moral restraints but concluded that this made no practical difference, since chemical and biological warfare in any future conflict would be directed against the United States “on the opening day.”

American public opinion, the OPD report optimistically concluded, easily could be shifted to accept gas warfare. “A program of education, stressing [that it is not worse than flamethrowers, phosphorus, or napalm] and that lives of … soldiers can be saved, will overcome this prejudice. Actually, there is considerable public demand to use gas,” the OPD emphasized. Support for gas warfare, near 40 percent according to public opinion polls, had been growing in the months since Iwo Jima.

By mid-1945, as Army planners knew, Japan had produced very little gas and, lacking air superiority, could not use it against American troops outside the main Japanese islands. While the United States had produced about 135,000 tons of chemical warfare agents, Germany about 70,000 tons, and Britain about 40,000 tons, Japan had only 7,500 tons. In brief, American production was 1,800 percent greater than Japan’s.

But if the Army viewed gas warfare as useful in softening Japan, the invasion plans did not hinge upon approval of gas warfare, and planners saw that the use of such a weapon could depend upon Allied agreement. Accordingly the OPD suggested that President Harry S. Truman discuss the issue with Joseph Stalin at Potsdam and then with Chiang Kai-shek.

In Washington, General Marshall sent the OPD report to the other military chiefs. There is no record of replies by Admiral King or by Gen. Henry H. (“Hap”) Arnold, chief of staff of the Army Air Forces. The Navy, in view of its faith in bombing and a blockade, had its own agenda for ending the war and was probably not supportive of Marshall’s plan.

Arnold had earlier rejected a gassing plan—”a quick knockout of Japan from the air by concentrating on sources of food,” partly by spraying mustard gas on rice-producing areas—on tactical rather than on moral or political grounds. As one of his aides had explained, “the effort to do a good job against food would be better expended against material objectives having earlier and certain impact.” Given limited resources, the Air Force preferred to continue its bombing of Japanese cities, which some Air Force generals thought might defeat Japan before the planned invasion in November.

Alone among the President’s top military advisers, Adm. William Leahy, the crusty, aged chief of staff to the Commander in Chief, opposed Marshall’s plan. And unlike many of the top brass, Leahy was not reluctant to raise fierce moral objections. Earlier he had opposed both gas and bacteriological warfare because, as he had told FDR in 1944, they “would violate every Christian ethic I have ever heard of and all of the known laws of war. It would be an attack on the noncombatant population of the enemy.” On June 20, 1945, replying sharply to Marshall, Leahy emphasized that Roosevelt had categorically barred first use of gas.

Apparently Marshall never brought his plans to Truman. The last important reference on the matter appears in an OPD briefing paper for the Potsdam Conference: “the advisability of changing the policy to permit the use of gas against the Japanese has been discussed informally by the Joint Chiefs of Staff. [Because the Allies might oppose such a reversal in policy], a decision to initiate use of gas must be taken on the highest level.”