The Bombs that Really Ended WWII

As viewed from America, credit for ending World War II in the Pacific regularly goes to the two atomic bombs that devastated Hiroshima and Nagasaki on August 6th and 9th, 1945. With justification, Russians are more likely to emphasize the importance of the Soviet Union as it declared war against Japan on August 8th and began to flood 1.6 million troops into Japanese-occupied Manchuria. These and other events were certainly important, but neither did as much to degrade Japan’s will and ability to continue the war as did America’s 6-pound M69 incendiary bombs. The final use of these and other incendiary munitions came later in the war than most people realize. It was not until August 14—just one day before Emperor Hirohito publicly announced Japan’s unconditional surrender—that American B-29s conducted their last incendiary attacks.

The man most responsible for M69 bombs and the strategy behind their use was J. Enrique Zanetti. He was born of Swiss heritage in the Dominican Republic on January 20, 1885 and immigrated to the U.S. with his family as a child. He graduated magna cum laude from Harvard in 1906 and continued at Harvard to earn a Ph.D. in chemistry in 1909. That same year, he became a member of the faculty at Columbia University. During the First World War, Zanetti was commissioned as a Captain in the U.S. Army Ordnance Department and sailed for France, assigned to what was then called the Gas Service. He was promoted in August 1918 to become a Major in the renamed and restructured Chemical Warfare Service (CWS). He was promoted again two months later to the rank of Lieutenant Colonel. Much of his work during WWI involved liaison with other Allied nations regarding methods for using mustard agent, phosgene and other toxic chemicals. Between the two World Wars, Zanetti returned to his faculty position at Columbia University, but he continued to serve in the CWS as a Reserve Colonel. He was very active during the inter-war period as an advocate for incendiaries, which many regarded as no more important than the smoke bombs for which the CWS was also responsible.

Incendiary weapons date back to the Middle Ages and beyond, including flaming balls of pitch thrown by catapults over castle walls. Most of Zanetti’s writings about how to modernize the technique were intended exclusively for military audiences and are difficult to obtain. One booklet, Fire from the Air: The ABC of Incendiaries, was published in 1941 for a wider audience that included firefighters. Zanetti felt American firefighters should be prepared to deal with advanced incendiaries delivered to American cities by enemy aircraft. He was aware too that America’s firefighting community could offer insights that would be useful to the military in preparing to use fire offensively.

Zanetti recognized as he wrote his booklet that the war in which America would soon be involved would be “all out,” with the concept of purely military targets giving way to a focus on cities as the objective to be attacked. He disagreed with most leaders of his Chemical Warfare Service in arguing that incendiaries, not toxic chemicals, would be the most effective weapon for attacking enemy cities. Much of his argument in favor of incendiaries was summarized in the brief phrase, “gas dissipates, fire propagates.” Unlike toxic or high-explosive bombs, even one small incendiary bomb had the potential (like Mrs. O'Leary’s cow) to ignite a city-destroying conflagration. Increasing the impact of incendiaries included a number of technical innovations such as the carefully calculated use of oxidizing agents within the bomb. Greater effectiveness, Zanetti also recognized, depended as well on carefully planned distribution of many incendiaries so that numerous small fires would merge and overwhelm the resources of local firefighters.

America’s M69 bombs were highly effective, particularly against Japanese cities. Each was designed to penetrate the roof of a building and continue through to the floor, from where it threw flaming napalm upwards and outwards. The napalm itself would continue to burn for several minutes, long enough to ignite virtually any flammable material. The 6-pound bombs were packed in various “aimable” clusters, which could be set to distribute the M69 bombs as widely or as tightly as desired. The success of incendiaries was demonstrated in Europe with attacks on Hamburg, Dresden and other cities, but the most dramatic success was the Tokyo Firestorm of March 9, 1945. The long-term effects of radiation from the atomic bombings of Hiroshima and Nagasaki may have ultimately resulted in more casualties. Still, the immediate effects of the Tokyo Firestorm remain undisputed as the single most deadly bombing raid in history.

The B-29 bombers of America’s XXI Bomber Command conducted raids during 1945 that included mine laying and other missions, but General Curtis LeMay kept the focus on strategic bombing of cities, believing that overwhelming air power could force Japan to surrender without the need for a land invasion. Although the 329th mission flown by the XXI has been largely ignored, it provides valuable insights into the overall results of LeMay’s strategy. On August 14—five days after the atomic bombing of Nagasaki and one day before Emperor Hirohito publicly announced Japan’s unconditional surrender—77 B-29s from the 314th Bomb Wing and 16 B-29s from the 313th Bomb Wing attacked Kumagaya. Kumagaya had a population of about 45,000 people, roughly similar to the current population of Midland, Michigan or Bozeman, Montana. The lead aircraft dropped six 1000-pound high-explosive bombs to create a dramatic airburst, apparently intending to convince Japan that the U.S. had dropped a third atomic bomb. The remaining bombers dropped 6321 100-pound M47 incendiary bombs, 356 M17 clusters (each containing 110 4-pound thermite-magnesium bombs) and 1372 M19 clusters (each with 38 M69 bombs). The resulting fires burned 74% of the city but resulted in relatively few human casualties. The low casualty rate was due at least partly to the initial airburst, which served (intentionally or not) as a warning to the people below of the incendiaries to come. According to correspondent Homer Bigart, the crews of the 314th were aware the war was virtually over, and they saw no reason to risk their lives to bomb “a pathetically small city of little obvious importance.” The bombers encountered no effective resistance from Japanese fighters or antiaircraft fire, and all returned safely to base.

There has been considerable discussion as to the number and timing of additional atomic bombs that the U.S. could have dropped if Japan had refused to surrender in mid-August. There is no question, however, that the U.S. still had a huge stockpile of incendiary bombs available for immediate use, a growing number of B-29s ready to deliver those bombs and the air and ground crews needed to conduct many more bombing raids. The primary challenge U.S. planners would have faced if they had been called upon to continue the incendiary missions was the shortage of suitable Japanese targets. The Chemical Warfare Service was also ready with a stock of toxic chemical munitions that far exceeded the quantity available during World War I. Even some leaders familiar with the Manhattan Project advocated for these to be used as a supplement to the atomic bombs. Fortunately, neither more atomic bombs nor more incendiaries nor the toxic chemical bombs nor the widely expected land invasion were necessary to end the war.

Zanetti and over 70,000 other soldiers who served in the U.S. Chemical Warfare Service during WWII deserve to be remembered.