The Fire Balloons

v1.0.1 / 01 jun 02 / greg goebel / public domain

* When General Jimmy Doolittle led his B-25 bombers in a sneak raid over Japan in the spring of 1942, he set into motion a chain of events that would result in one of the more bizarre stories of World War II: the Japanese attempt to attack the continental United States by bomb-carrying balloons, floating across the entire Pacific Ocean.

From the late fall of 1944 through the early spring of 1945, the Japanese launched more than 9,000 of these "fire balloons", of which 300 were found or observed in the US. Some guesswork gives the total number that made the trip at about 1,000. Despite the high hopes of their designers, the balloons were totally ineffective as weapons, and survive in memory only as an ingenious and malevolent curiosity.

This document provides a short history of the Japanese fire balloon offensive against America.



* The Japanese performed a small number of attacks on the American mainland through World War II. In February 1942, Japanese Submarine I-17 shelled an oil field up the beach from Santa Barbara and damaged a pump house. That following June, Submarine I-25 shelled a coastal fort in Oregon, damaging a baseball backstop, and in September, that submarine's crew assembled and launched a small float plane that dropped incendiary bombs, starting a few small forest fires.

The fourth and final attack, using balloons carrying incendiary bombs, was the most earnest of them all. The concept was the brainchild of the Japanese Ninth Army Technical Research Laboratory, under Major General Sueyoshi Kusaba, with work performed by Technical Major Teiji Takada and his colleagues. The balloons were intended to make use of a great strong current of winter air that the Japanese had discovered flowing at high altitude and speed over their country, which would someday be known as the jet stream.

The jet stream blew at altitudes above 9.15 kilometers (30,000 feet) and could carry a large balloon across the Pacific in three days, over a distance of more than 8,000 kilometers (5,000 miles). Such balloons could carry bombs to the United States and drop them there to kill people, destroy buildings, and start forest fires. In this way the Japanese would punish the impudence of the Americans for the Doolittle raid against Tokyo and other Japanese cities in 1942. They named the weapon "fusen bakudan", which literally means "fire bombs", but which has been translated as "fire balloons".

Building a balloon that could survive a trip across the Pacific and then automatically drop its warload was technically challenging. A hydrogen balloon expands when warmed by the sunlight and rises, then contracts when cooled at night and falls. The engineers devised a control system driven by an altimeter that discarded ballast to maintain altitude.

When the balloon descended below 9 kilometers, it electrically fired a charge to cut loose sandbags. The sandbags were carried on a cast-aluminum four-spoked wheel, and discarded two at a time to keep the wheel balanced. Similarly, when the balloon rose above about 11.6 kilometers (38,000 feet), the altimeter activated a valve to vent hydrogen. The hydrogen was also vented if the balloon's pressure reached a critical level.

The control system ran the balloon through three days of flight. At that time, it was likely over the United States, its ballast expended. The final flash of gunpowder released the bombs, also carried on the wheel, and lit a 19.5 meter (64 foot) long fuze that hung from the balloon's equator. After 84 minutes, the fuze fired a flash bomb that destroyed the balloon.

The balloon had to carry about 900 kilograms (1,000 pounds) of gear, which meant a hydrogen balloon with a diameter of about 10 meters (33 feet). At first, the balloons were made of conventional rubberized silk, but there was a better way to make an envelope that leaked even less. An order went out for ten thousand balloons made of "washi", a paper derived from mulberry bushes that was impermeable and very tough. It was only available in squares about the size of a road map, so it was glued together in three or four laminations using paste derived from a tuber with the Japanese name of "devil's-tongue".

Hungry workers stole the paste and ate it. Many workers were teen-aged girls, whose fingers were nimbler than any class of people. They were told to wear gloves, to keep their fingernails short, and not to use hairpins. They assembled the paper in many parts of Japan. Large indoor spaces, such as sumo halls, soundstages, and theatres were required for the envelope assembly.

The workers had no idea of the purpose of their work. When rumors suggested the truth to them, that they were making "fusen bakudan" that would fly all the way to America and start fires, they laughed. Somehow, secrecy was preserved.



* Initial tests took place in September 1944, and proved satisfactory. However, before preparations were complete, B-29s began their raids on the Japanese home islands. The attacks were somewhat ineffectual at first, but still fueled the desire for revenge sparked by the Doolittle raid.

The first balloon was released in early November 1944. Major Takada watched as the balloon flew upward and over the sea: "The figure of the balloon was visible only for several minutes following its release until it faded away as a spot in the blue sky like a daytime star."

* By early 1945, Americans were becoming aware that something strange was going on. Balloons had been sighted, explosions heard, from California to Alaska. Something that appeared to witnesses to be like a parachute descended over Thermopolis, Wyoming. A fragmentation bomb exploded and shrapnel was found around the crater. A P-38 Lightning shot a balloon down near Santa Rosa, California; another was seen over Santa Monica; and bits of washi paper were found in the streets of Los Angeles.

Two paper balloons were recovered in a single day in Modoc National Forest, east of Mount Shasta. Near Medford, Oregon, a balloon bomb exploded in a gusher of flame. The Navy found balloons in the ocean. Balloon envelopes and apparatus were found in Montana, Arizona, Sasketchewan, in the Northwest Territories, and in the Yukon. Eventually, an Army fighter managed to somehow push one of the balloons around in the air and force it to ground intact, where it was examined and filmed.

NEWSWEEK ran an article titled "Balloon Mystery" in their 1 January 1945 issue, and a similar story appeared in a newspaper the next day. The Office of Censorship then sent a message to newspapers and radio stations to ask them to make no mention of balloons and balloon-bomb incidents, lest the enemy get the idea that they had a good thing going.

* The fact that the balloons had been launched beginning in the fall made them little menace. The incendiary bombs could have caused forest fires, but by that time of year forests were generally too damp to catch fire easily.

However, the authorities were worried about the balloons anyway. There was the chance that they might get lucky. Much worse, the Americans had some knowledge that the Japanese had been working on biological weapons, most specifically at the infamous Unit 731 site at Pingfan in Manchuria, and a balloon carrying biowarfare agents could be a real threat.

Nobody believed the balloons could have come directly from Japan. It was thought that the balloons must be coming from North American beaches, launched by landing parties from submarines. Wilder theories speculated that they could have been launched from German prisoner of war camps in the US, or even from Japanese-American internment centers.

Some of the sandbags dropped by the fusen bakudan were taken to the Military Geology Unit of the US Geological Survey for investigation. This team had been established in June 1942, six months after Pearl Harbor. Geological Survey people wanted to get involved in the war effort, either for the patriotism or prestige or both, and provided a geological intelligence report for a randomly chosen country, Sierra Leone.

The report described the terrain, locations of water supplies and road-building materials, and other obviously useful facts. The military bought the idea and so the Military Geological Unit was formed, starting out with six people but quickly expanding.

Working with Colonel Sidman Poole of US Army Intelligence, the researchers of the Military Geological Unit began microscopic and chemical examination of the sand from the sandbags to determine types and distribution of diatoms and other microscopic sea creatures, and its mineral composition. The sand could not be coming from American beaches, nor from the mid-Pacific. It had to be coming from Japan.

In the meantime, the balloons continued to arrive in Oregon, Kansas, Iowa, Manitoba, Alberta, Northwest Territories, Washington State, Idaho, South Dakota, Nevada, Colorado, Texas, northern Mexico, Michigan, and even the outskirts of Detroit. Fighters scrambled to intercept the balloons, but they had little success; the balloons flew very high and surprisingly fast, and the fighters destroyed fewer that 20.

The geologists continued their studies, and ultimately determined the precise beaches in Japan the sand had been taken from. By this time, it was mostly irrelevant, since by early spring the balloon offensive was almost over.

The balloons did kill six Americans. A minister and his wife had taken some children on a fishing trip in southern Oregon, east of the Cascades, when they discovered a balloon bomb that exploded while they were gathered around it, killing the woman and five children. Japanese propaganda broadcasts announced great fires and an American public in panic, declaring casualties as high as 10,000, but the six people killed in Oregon were the only casualties inflicted by the enemy on the American mainland in World War II.

* The press blackout was lifted after the deaths to ensure that the public was warned. However, even without the press blackout, the Japanese would have had no reason to believe they had accomplished anything of significance.

General Kusaba's men launched more than 9,000 balloons, of which about 300 were reported in the US. The Japanese estimated that about 10% would complete the trip, and in fact it is likely about a thousand did so. Two landed back in Japan, but caused no damage.

The expense of the program was great, and in the meantime the ever more fearsome B-29s had destroyed two of the three hydrogen plants needed by the project. With no evidence of any effect, General Kusaba was ordered to cease operations in April 1945.

On 10 March 1945, one of the last paper balloons had descended in the vicinity of the Manhattan Project's production site at Hanford, Washington. The balloon landed on a power line that fed electricity to the building containing the reactor producing plutonium for the Nagasaki bomb, and shut the reactor down.



* The main source for this article was:

Additional details were provided by the History Channel's SECRETS OF WORLD WAR II series, which included an installment titled "Japan's Last Secret Weapons" that included the fusen bakudan, kamikaze aircraft, and the "kaiten" kamikaze submarines.

* Revision history:

   v1.0   / 01 feb 00 / gvg
   v1.0.1 / 01 jun 02 / gvg / Minor cosmetic update.