In June 1945, as the Pacific war continued its bloody advance toward the Japanese Home Islands, President Harry S. Truman met in the White House with his senior military and civilian advisers to plan the strategy for ending the conflict. The decision reached was to invade the Japanese homeland, the southern island of Honshu on 1 November 1945, and the main island of Honshu in the spring of 1946. American casualties in the two assaults and drive on Tokyo would likely number hundreds of thousands of dead and wounded. In the offing were the atomic bombs.
During the summer of 1945 still another means of attacking Japan was being discussed—poison gas. Earlier, the U.S. and British governments had agreed that they would employ poison gas only in retaliation if an enemy used it first. Japan already had used poison gas in China, and Nazi Germany had gassed millions of Jews.1 Moreover, many Americans were advocating using poison gas against Japan. On 11 March 1945, while U.S. troops were fighting on Luzon and Iwo Jima with heavy loss of life, the Chicago Tribune ran an editorial headlined “You can cook them with Gas.” It declared that the charge that poison gas “is inhumane is both false and irrelevant. . . . The use of gas might save the lives of many hundreds of Americans and of some of the Japanese as well.”
In great secrecy the U.S. Army had been developing and storing poison-gas munitions in the Pacific theater. The Army and Navy had major gas-storage depots in Australia and Hawaii and smaller ones on Pacific islands. By mid-1945 similar poison-gas depots were being prepared north of Manila on Luzon and on Okinawa.
A 35-page June 1945 report by the Army’s Chemical Warfare Service stated that a major study had been undertaken to “determine whether or not gas should be used” in the invasion of Japan and “if so, when its use should be initiated.”2 The recommendations in the document were based on large?scale tests at the Dugway Proving Ground in Utah and on San Jose Island off Panama.
At the time of the study, the United States was producing poison gas at a prodigious rate. On hand by the end of 1945 would be more than 4.4 million gas artillery shells, 1 million gas mortar rounds, 1.25 million gas aerial bombs, and 112,000 tanks for spraying poison gas from low-flying planes.3
Mustard-gas land mines also were being produced in American factories. These were rectangular, one-gallon tin cans. Ten pounds of sulfur mustard in the can was detonated by a slow-burning fuse or electrical current, and the resulting gas would spread over a considerable area. These were intended as booby traps or for contaminating fields, roads, or buildings after U.S. troops landed in Japan. The Army procured and stored, but did not fill, almost two million such mines. Still, by April 1945 there were more than 43,000 of them in Pacific stockpiles.
Much of the thinking behind the poison-gas attack study had come from a meeting of Army planners on 12 October 1944, when Major General William Porter, the head of the Chemical Warfare Service, estimated that an attack “on a congested city area” would produce 10 percent casualties—an “impact never yet attained in this war by air attack or robot bombs [German V-1 flying bombs and V-2 ballistic missiles].”
The Army planners selected 50 “profitable urban and industrial targets” in Japan, with 25 cities listed as “especially suitable for gas attacks.” These targets included Hiroshima and Nagasaki. The study declared, “Gas attacks of the size and intensity recommended on these 250 square miles of urban population . . . might easily kill 5,000,000 people and injure that many more.” Each city was divided into zones based on population density. The greater the concentration of people, the better the zone as a gas target.
The largest poison-gas raid should be on Tokyo because an “attack of this size against an urban city of large population should be used to initiate gas warfare.” The planners targeted 17.5 square miles directly north of the Imperial Palace and west of the Sumida River—an estimated 948,000 people were in that area. Within two miles of the target area were another 776,000 people who probably would be in the path of wind-carried gas. Ironically, the size of the targeted area was almost exactly the same size as the area of Tokyo burned out by the B-29 firebombing on the night of 9–10 March 1945.
The study recommended launching the gas attack on Tokyo at 0800, when the greatest number of people would be concentrated in the city. Bombers would drop either 21,680 500-pound gas bombs or 5,420 1,000-pound gas bombs, depending on the availability of the weapons. All of the bombs would be filled with phosgene.
Also called carbonyl chloride, phosgene is a colorless liquid, slightly denser than water, that boils at 47 degrees Fahrenheit, and hence in warm weather is a vapor unless under slight pressure, such as in a sealed bomb or artillery shell. The vapor dissipates into the air in a few minutes and when inhaled damages the capillaries in the lungs, allowing watery fluid to seep into the air cells. Large amounts flood the lungs, and the victim dies from a lack of oxygen. Phosgene caused more than 80 percent of all chemical fatalities in World War I.
During the subsequent attacks on other Japanese targets, the study recommended using three other types of gas:
• Hydrogen cyanide, a colorless liquid that evaporates quickly at room temperature. The gas interferes with normal processes of the respiratory center of the nervous system; if present in more than a small concentration it quickly kills.
• Cyanogen chloride, also a colorless liquid, boils at 55 degrees Fahrenheit to give off a vapor that irritates the eyes and nasal passages. Air containing a high concentration of the gas can quickly and fatally paralyze a victim’s nervous system. Low levels of the compound can accumulate in the body to a lethal concentration.
• Mustard gas, or sulfur mustard, another World War I weapon, is an oily brown liquid that evaporates slowly, giving off a vapor five times heavier than air that is almost odorless although in high concentrations smells like garlic or mustard. It mainly attacks the skin, soaking through clothes and causing painful blisters. The inhalation of the gas injures the respiratory tract and causes poisoning.
The study proposed that in direct support of the Army-Marine invasion of Kyushu, cyanogen chloride bombs be dropped on Japanese troop formations around Kagoshima, the island’s chief city, although it speculated that raids on reserve troops would “produce large numbers of casualties among the unprotected urban population of Kagoshima.” The report continued, “Gas attacks should be coordinated with the ‘softening up’ bombardment of the beaches prior to landing.” The American plan was based on extremely detailed analyses of cities, even addressing the width of streets and the locations of parks.
No known military plan from World War II addressed such wholesale killing of enemy troops and civilians. The proposed U.S. gas attack on Japan was a military action, designed in the words of the proposal, to “disrupt national life in Japan” just before and during the U.S. invasion. But in the end, the atomic bombings of Hiroshima and Nagasaki rendered moot an invasion of Japan and possible use of poison gas.
1. Before World War II, in 1934–35, Italy had used poison gas in its conquest of Ethiopia, and several countries used poison gas extensively in Europe during World War I.
2. “A Study of Possible Use of Toxic Gas in Operation Olympic,” submitted to the Chief, Chemical Warfare Service, U.S. Army, 9 June 1945. The gas-attack documents were released under a Freedom of Information Act request made by Norman Polmar and Thomas B. Allen, who had discovered the existence of the poison-gas study while researching their book Code-Name Downfall (Simon & Schuster, 1995) about the U.S. plan to invade Japan in 1945–1946.
3. Leo P. Brophy et al., The Chemical Warfare Service: From Laboratory to Field (Washington, DC: Center of Military History, U.S. Army, 1988), 65.
Rewriting the Study
In 1947 U.S. Army officials added a secret directive to the gas-attack study: If the report ever was declassified, it should be retyped and the word “retaliatory” frequently inserted to make it agree with announced U.S. wartime policy. As announced during the war, U.S. policy called for the use of poison gas only in retaliation.
To preserve the appearance of that policy, the 1947 Army directive ordered that the report be downgraded at the time from top secret to the next lower classification, secret. The retyping never happened, but the basic released document in possession of the authors has inked-in changes made in 1947, adding the word “retaliatory.”
During World War II, the U.S. policy regarding gas weapons officially was based on the Washington Naval Treaty of 1922. While concerned mainly with limiting warship construction and fortifications in the Pacific, the agreement prohibited the use of chemical weapons, except in retaliation. This treaty served as the basis for the Geneva Protocol of 1925, which outlawed the use of chemical and biological weapons but did not halt their production or possession. The Geneva accord also permitted retaliation with gas weapons. The United States signed the protocol, as did Japan, but did not ratify the pact until 22 January 1975.
—Norman Polmar and Thomas B. Allen