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


Forty years ago, on August 6 and 9, 1945, American B-29s dropped two atomic bombs on Japan, killing at least 110,000 and possibly 250,000 Japanese and speeding that nation’s surrender. During four years of bitter fighting, World War II had become for the United States virtually total war, in which morality had slowly been redefined to allow the intentional bombing of civilians.

Ever since, however, use of these atomic weapons has raised troubling questions about American ethics during the war. Yet lost in the concern is a related question: Why didn’t the United States also initiate gas warfare? Did an older sense of morality, rooted in the decades before Pearl Harbor, bar this form of war even as other moral constraints eroded?

During World War II, international law did not actually bar the United States from using gas warfare—although America had signed the 1925 Geneva Protocol outlawing gas, the Senate had never ratified it. Yet every peacetime President from Warren G. Harding to Franklin D. Roosevelt had defined gas as immoral and pledged to abide by the agreement. The cruel gas deaths of World War I, painfully etched in memory, constituted a powerful ethical deterrent. In a secret memo, written soon after Pearl Harbor, Secretary of State Cordell Hull, a Tennessee Democrat and proud Wilsonian, urged the administration to declare unilaterally that it would continue to observe this prohibition. Secretary of the Navy Frank Knox, a Chicago Republican, readily agreed: “The Navy is against the use [of gas] in wartime.”

But Secretary of War Henry L. Stimson, the leading Republican in the bipartisan war cabinet, opposed Hull’s proposal. Any public statement, Stimson contended, might provoke a domestic debate on moral and political issues that would delay military production of gas and lead Germany and Japan to view America as weak. Stressing that these enemies, as well as Italy, had repeatedly violated treaties, and claiming that Italy had used gas in Ethiopia and that Japan had done so in China, Stimson concluded that “the only deterrent is fear of our retaliation. I strongly believe that our most effective weapon on this subject at the present time is to keep our mouths tight shut.”

Events soon undercut this cautious strategy of silence. In May 1942 Prime Minister Winston Churchill, fearing German gas warfare against Russia, publicly warned Adolf Hitler that Britain would retaliate with gas on German cities. The next month President Roosevelt, citing new accusations against Japan, issued a similar warning: “If Japan persists in this inhuman form of warfare against China or against any other of the United Nations, such action will be regarded by this Government as though taken against the United States, and retaliation in kind and in full measure will be meted out.”

For Churchill, an ardent advocate of poison gas in World War I and never committed to the subsequent moral code against it, and for Roosevelt, sincerely committed to that code, the warnings were designed to deter enemies from launching gas warfare and thus making retaliation necessary. Roosevelt continued to receive reports of scattered incidents of Japanese gas warfare against China, but he and his advisers correctly interpreted these abuses as decisions made by local commanders, not as a statement of a new Japanese policy. Had the President been seeking a pretext to retaliate with gas, he might have seized upon these reports. But his caution and his moral inclinations reinforced each other, and he preferred instead to issue warnings and hope for the best.


In June 1943, using a State Department draft, Roosevelt sharply reaffirmed United States policy on gas warfare: “Use of such weapons has been outlawed by the general opinion of civilized mankind. This country has not used them, and I hope we never will be compelled to use them. I state categorically that we shall under no circumstances resort to the use of such weapons unless they are first used by our enemies.” Such a ringing statement of morality, even as the barbarities of war chipped away at other parts of the international military code, made it unlikely that FDR would yield easily to entreaty or to the claim of exigency.

His known opposition to initiating gas warfare blocked some American military planners from seriously considering it and thus deterred the very bureaucratic actions that might have pressed him to reconsider his commitment. He also received indirect support from the Navy and Army Air Force. Top Navy officials had concluded that gas should not be used against civilian populations and that it was not especially effective against military targets. “Hit for hit and pound for pound,” said Adm. Ernest King, chief of naval operations, “no service chemical is considered to offer as great effectiveness as high explosive.” Air Force leaders, committed to aerial bombing, had reached a similar conclusion.

Even so, the budget and total personnel of the Army’s Chemical Warfare Service (CWS) soared. Held to an average annual appropriation of $1.5 million and to about five hundred Army personnel through the mid-thirties, in 1942 the CWS received one billion dollars and had more than sixty thousand employees. Its tasks included preparing for gas and bacteriological warfare, as well as producing incendiaries for bombing, flamethrowers, and other devices.