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I. The Fu-go Project

July 2024
9min read

A bomb-laden balloon from Japan reached North America, resulting in the only death from enemy action during the war.

On August 3, 1976, a retired Japanese scientist made a pilgrimage to a World War II battlefield shrine. Accompanied by a small group of Americans from the nearby lumbering community of Bly, Oregon, Sakyo Adachi climbed a secluded woodland slope and stopped before a monument built of native stone. While the others watched, Adachi placed a floral wreath below an inscription that reads:


Then he stepped back, pressed his palms together in a gesture of prayer, and bowed. His American companions grasped his hands in friendship.

The people being memorialized had been killed by a weapon that linked the technology of twentieth-century warfare with an ancient object of fragile grace.

In the early daylight hours of April 18, 1942, the carrier Hornet , steaming several hundred miles off the Japanese coast, headed into the wind as, one by one, sixteen B-25’s lifted off her rolling deck. Flying low and in brilliant daylight, all sixteen planes reached their targets and unloaded incendiary bombs on Kōbe, Nagoya, Yokosuka, and Tokyo. The physical damage inflicted by James H. Doolittle’s spectacular raid was negligible,'but it shook the Japanese Imperial High Command: the homeland had been violated, and honor demanded retaliation upon America.

For more than a decade Japanese meteorologists had been aware of air currents high overhead that traced a serpentine pattern eastward. Would it be possible for these currents, later to be called “jet streams,” to carry free-floating balloons that could bomb the forests, farm lands, and cities of the United States? The idea seemed preposterous. But Japanese scientists had been experimenting with hydrogen-filled balloons since the early 1930’s, and they had solved some formidable technical problems. So by 1943, when military leaders ordered a face-saving counter-attack, the balloon specialists already had their “Fu-Go” project under way. They were close to perfecting a weapon that would travel sixty-two hundred miles toward a target area, drop its payload of bombs, and then destroy itself, entirely under its own power.

The first bomb-laden balloons lifted off the Japanese mainland on November 3, 1944. If all went as planned, heat from the sun’s rays would cause the hydrogen in the bag to expand, raising each balloon to its highest altitude, approximately thirty-eight thousand feet. There it would meet the winter winds coursing northeastward at speeds often exceeding two hundred knots. At night, when temperatures dropped to minus 50 degrees Centrigrade and the contracting gas pitched the craft about three thousand feet, a specially developed altitude-control device would discharge enough ballast to lighten the balloon, maintaining a minimum altitude of thirty thousand feet. Next day the sun would again warm the gas and the balloon would ascend to repeat its vaulting cycle. By the time the craft reached the American Northwest, all its ballast would have been dropped. The altitude mechanism would then begin discharging bombs instead of sandbags. The estimated sailing time from Japan to the United States was sixty hours.

During the last weeks of 1944 the U.S. Western Defense Command began receiving reports of paper balloons, or fragments of them, landing in scattered areas across the American Northwest. At first they were thought to be Japanese weather or antiaircraft barrage balloons that had accidentally drifted across the Pacific. By the end of December, however, sightings grew more frequent, and the Naval Research Laboratory and the FBI set out to determine the origin and objective of the balloons. Investigators already knew that the balloons were Japanese and, in some cases, when they were constructed and even where they were launched. Early in the new year they would discover their purpose.

On January 4, 1945, two men working in a field about a mile southwest of Medford, Oregon, were startled by a strange aerial whine. Within seconds there was an explosion nearby, and a thirty-foot column of flame shot skyward. When investigators arrived, they found a charred hole six inches wide and twelve deep and the remains of an incendiary bomb. Since no aircraft had been heard, the source of the bomb remained a mystery until someone found a hook nearby, identical to ones discovered among fragments of the peculiar balloons now being reported in alarming numbers. The origin of the mysterious bomb became apparent: Japanese balloons were bombing the United States.

The U.S. Office of Censorship immediately quashed the story. News agencies were requested to refrain from publishing reports of the balloon operations for fear that if the Japanese knew their bombs were reaching North America, they would redouble their attacks.

A few days after the Medford, Oregon, explosion, a Navy P-38 Lightning was dispatched to intercept a balloon drifting high over Alturas, California. Employing British antibuzz-bomb tactics, the pilot used his plane’s slip stream to force the balloon to a lower altitude, where he laced the bag with machine-gun bullets. It gradually lost gas, settled gently, and was recovered with all its remaining ballast, bombs, and release mechanisms intact. The entire balloon was shipped to Moffett Field, Sunnyvale, California, where it became the basis for the Western Defense Command’s first detailed report on the new weapon.

The confidential study noted that the bags were made of sections of paper, layered and glued with a paste manufactured from konnyaku , a common potatolike vegetable. The bags, which measured a shade under thirty-three feet in diameter, were connected to the undercarriage by nineteen 49-foot shroud lines. The undercarriage contained a single-cell 2.3-volt battery, an altitude-control device, a ballast-discharging mechanism, a ring of thirty-two sandbags, and five bombs—including four incendiaries and one fragmentation. Each undercarriage carried a two-pound demolition block of picric acid designed to destroy the mechanism in midair after it had completed its mission. Finally each balloon bag carried a flash bomb attached to the undercarriage by a 64.5-foot fuse. When the undercarriage exploded, this long fuse would burn until it ignited the hydrogen, producing a brilliant airborne explosion.

The ordnance they carried suggested the balloon bombs’ primary strategic mission was to wage an incendiary war against the rich forests of the American Northwest. Upon impact, each fire bomb would disperse a flaming chemical and had the potential of destroying hundreds of acres of woodland. If the Fu-Go mission had been entirely successful, the Imperial Command would have unloaded fifteen thousand antipersonnel bombs and sixty thousand incendiary bombs on the United States. But although more than three hundred and fifty balloons were documented as having reached the continent, few caused any significant fire damage, for their targets were frozen and often snow covered. Only during the winter were the westerly winds powerful enough to sweep the balloons across the Pacific in the three days the craft could be expected to remain aloft.

But what if physical destruction was not the primary objective of the balloon bombs? Even the most idealistic of Japan’s wartime planners knew that their balloons could not destroy the American military machine. But as they observed the psychological effects of American bombing raids on their civilian populations, they became increasingly aware of how vulnerable a nation under stress could be. Enemy bombers coming out of the sky are fearsome weapons; but at least their coming can be seen and heard. The Fu-Go balloons, on the other hand, were capricious: they drifted silently, unpredictably, far beyond sight of the naked eye. Their bombs descended mysteriously, from an unknown, faceless enemy, presumably leaving their victims prey to hidden fears, to vague suspicions, and even to mass hysteria.

And they were mysterious, these weapons. After the balloons had dropped the last of their payload, they would ignite themselves in a celestial grand finale. This fashioned a blazing extraterrestrial phenomenon, and throughout the winter months of 1944-45, Western farmers and ranchers reported seeing bright, stationary fireballs in the skies, while, on December 8, 1944, the Northern Wyoming Daily News reported that a “Phantom Plane” was being sought after a series of explosions illuminated the night sky. The mystery was later solved when Naval Research Laboratory investigators determined that bomb and paper fragments found in the area had Japanese origins.

The balloons failed to inspire widespread panic but they did succeed in stirring grave fears among U.S. government officials, who foresaw the possibility of a disaster of unimaginable scope. One military historian, who believes the primary purpose of the balloon bombs was to spread fire, describes their “second most logical purpose” as the introduction of biological warfare. “The intense cold (minus 20 to minus 50 degrees Centigrade) at the altitude of the balloon flights,” wrote Cornelius W. Conley in the February/March 1968 issue of Air University Review , “would facilitate the transmission of bacteria, and disease germs affecting humans, animals, crops and forests could be transported.… It would be theoretically possible to infect the vast U.S. culcine (mosquito) population and establish a permanent endemic focus of an agent.”

Consequently, state health officers, veterinarians, agricultural agents, and 4-H Clubs were among those mobilized, under the code name “Lightning Project,” to be on the lookout for possible epidemics or poisonings. Decontamination squads were trained, and the government set up detailed procedures for collecting information, for dealing with reports, and especially for keeping a tight lid on the story.

There is no evidence that the Japanese loaded the balloons with harmful bacteria. General Sueki Kusaba and Technical Lieutenant Commander Kiyoshi Tanaka, leaders of the balloon bomb project, have consistently maintained that they never planned to engage in biological or chemical warfare.

The Fu-Go project ended early in April, 1945, after thousands of launchings. Historians have extolled American newspaper and radio editors for their discretion, which allegedly prevented the Japanese from knowing that their balloons were reaching the United States. On May 29, 1947, The New York Times declared: “Japan was kept in the dark about the fate of the fantastic balloon bombs because Americans proved during the war they could keep their mouths shut. To their silence is credited the failure of the enemy’s campaign.”

That silence did not long survive the six American deaths near BIy, Oregon, on May 6, 1945—nearly a month after the last balloons had lifted off Japanese soil. On May 7 the Klamath Falls (Oregon) Herald and News reported that Elsie Mitchell and five children had been killed while on a fishing trip by an explosion of “unannounced cause.” “One of the party found an object,” it continues, “others went to investigate, and the blast followed.” There were no other details. There was no speculation in the news media about the cause of the explosion. Further reports were limited to a single account of a mass funeral for four of the blast victims. Two weeks later the government abandoned its censorship campaign and the Navy and War departments issued a joint statement describing the nature of the balloon bombs, and warning people to avoid tampering with strange objects. Because the attacks were “so scattered and aimless,” it was believed they posed no serious military threat to the United States. The announcement stressed “that the possible saving of even one American life through precautionary measures would more than offset any military gain occurring to the enemy from the mere knowledge that some of his balloons actually have arrived on this side of the Pacific.”

In 1949 the soundness of the censorship campaign was further questioned when the U.S. Congress approved a bill providing compensation of twenty thousand dollars to the families of those killed at BIy. Although the Senate Judiciary Committee maintained that no Army personnel were directly responsible for the deaths, it insisted that the Army and other services were “aware of the danger from these Japanese bombs and took no steps, for what may have been valid reasons, toward warning the civilian population of the danger involved.”

Although the American news black-out rendered it difficult for the Japanese to assess the effectiveness of their Fu-Go project, it was not the principal cause for the termination of the mission.

By April of 1945 Japanese ground crews suspended further balloon launchings because American B-29’s were destroying important hydrogen sources. General Kusaba reported: “To my great regret, the progress of the war was faster than we imagined. Soon after the campaign began, the air raids against our mainland were intensified. Many factories that manufactured various parts were destroyed. Moreover, we were not informed about the effect of Fu-Go throughout the wartime. Due to the combination of hardships we were compelled to cease operations.”

In the five months that they drifted over American soil, what did the balloon bombs accomplish? Was the mission, as The New York Times described it, a “humiliating failure” that should have been awarded “first prize for worthless war weapons”?

The total cost of the Fu-Go project has been estimated at $2,000,000, with each balloon estimated at $920. Thus, in comparison with other military weapons, the balloon bomb was remarkably inexpensive, and one historian has assessed the campaign as an economic success that “gave the Japanese a good return on their investment.” The bombs, he continues, “were a headache for Canadian and American military and security people and created more paperwork and disrupted more routine than any other Japanese attack against the North American mainland. … The money, material, and effort expended in defense and investigation caused more time and monetary damage to the Allied war effort than the two million dollars the Japanese spent to build, equip, and launch the balloons.”

The Army had to train a large number of soldiers for the “Fire Fly Project,” an extensive plan to combat forest fires. By May of 1945 American Forest Service personnel in the Northwest were supported by three thousand Army troops, including the 555th Parachute Infantry, a battalion of three hundred combat-ready paratroopers, backed up by thirty-nine airplanes.

And in one instance, the Fu-Go project came close to achieving an effect beyond the wildest hopes of the Japanese.

At the Hanford Engineering Works in the state of Washington, a project of utmost secrecy was taking place: huge reactors were turning out radioactive uranium slugs that were to be used to manufacture plutonium for atomic bombs. Engineers had taken extraordinary precautions to prevent a variety of possible mishaps, but the one they most feared was a cutoff of water needed to keep the reactors at safe operating temperatures. Electrical power for the cooling pumps came from generators at the Bonneville or Grand Coulee dams. Interruption of flow for even a fraction of a second would create such a build-up of heat that the reactor might collapse or explode.

Suddenly, on March 10, 1945, the worst happened: a power failure occurred. Immediately, safety controls were triggered and current resumed, but the entire plant was shut down for one-fifth of a second. It took scientists three days to bring the reactor piles back up to full capacity, but they welcomed the incident because, as one witness later reported, “it proved that all safety arrangements, never before tested in an actual crisis, were working beautifully.”

An accident of calamitous proportions had been averted, but what caused the mysterious shutdown? A Japanese balloon, descending upon the Hanford area, had become tangled in electrical transmission lines, short-circuiting the power for the Hanford reactor pumps.

The Japanese could scarcely have suspected how their simple Fu-Go campaign disrupted the Manhattan Project, the most complex and expensive scientific enterprise yet conceived. It was a single paper balloon that nearly unleashed the furies of the nuclear age on the United States only months before they were visited upon the cities of Hiroshima and Nagasaki.

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