Fire balloons or balloon bombs (Japanese 風船爆弾 fūsen bakudan, lit. "balloon bomb") were hydrogen balloons with a load varying from a 12 kg (26 lb) incendiary to one 15 kg (33 lb) antipersonnel bomb and four 5 kg (11 lb) incendiaries attached. They were launched by Japan during World War II, designed to wreak havoc on Canadian and American cities, forests, and farmlands.
Japanese bomb-carrying balloons were 10 meters (33 ft) in diameter and when fully inflated, held about 540 cubic metres (19,000 ft³) of hydrogen. Launch sites were located on the east coast of the main Japanese island of Honshū.
Similar, but cruder, balloons were also used by Britain to attack Germany between 1942 and 1944.
When Lieutenant Colonel Jimmy Doolittle (later General) led his B-25 bombers in a sneak raid over Japan in early 1942, he set into motion a chain of events that resulted in one of the more bizarre stories of World War II: the Japanese attempt to attack North America by bomb-carrying balloons, floating across the entire Pacific Ocean.
From late 1944 until early 1945, the Japanese launched over 9,000 of these fire balloons, of which 300 were found or observed in the U.S. Some guesswork gives the total number that made the trip at about 1,000. Despite the high hopes of their designers, the balloons were relatively ineffective as weapons, causing only six deaths and a small amount of damage, and they survive in memory mostly as an ingenious and dangerous curiosity.
Japan released the first of these bomb-bearing balloons on November 3, 1944. They were found in Alaska, Washington, Oregon, California, Arizona, Idaho, Montana, Utah, Wyoming, Colorado, Texas, Kansas, Nebraska, South Dakota, North Dakota, Michigan and Iowa, as well as Mexico and Canada. The last one was launched in April 1945. The last known discovery of a functional fire balloon in North America was in 1955 - its payload still lethal after 10 years of corrosion. A non-lethal balloon bomb was discovered in Alaska in 1992.
The bombs caused little damage, but their potential for destruction and fires was large. The bombs also had a potential psychological effect on the American people. The U.S. strategy was to not let Japan know of the balloon bombs' effectiveness. Cooperating with the desires of the government, the press did not publish any balloon bomb incidents. As a result, the Japanese only learned of one bomb reaching Wyoming, landing and failing to explode, so they stopped the launches after less than six months.
The balloon campaign was the fourth attack the Japanese had made on the American mainland. The fūsen bakudan campaign was, however, the most earnest of the attacks. 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 strong current of winter air that the Japanese had discovered flowing at high altitude and speed over their country, which later became known as the jet stream.
The jet stream blew at altitudes above 9.15 kilometers (30,000 ft) and could carry a large balloon across the Pacific in three days, over a distance of more than 8,000 km (5,000 mi). Such balloons could carry incendiary and high-explosive bombs to the United States and drop them there to kill people, destroy buildings, and start forest fires.
The preparations had consumed much time because the technological problems were acute. A hydrogen balloon expands when warmed by the sunlight, and rises; then it contracts when cooled at night, and falls. The engineers devised a control system driven by an altimeter to discard ballast. When the balloon descended below 9 km (29,500 ft), it electrically fired a charge to cut loose sandbags. The sandbags were carried on a cast-aluminium four-spoked wheel and discarded two at a time to keep the wheel balanced.
Similarly, when the balloon rose above about 11.6 km (38,000 ft), 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, and its ballast was expended. The final flash of gunpowder released the bombs, also carried on the wheel, and lit a 19.5 meter (64 ft) long fuse that hung from the balloon's equator. After 84 minutes, the fuse fired a flash bomb that destroyed the balloon.
The balloon had to carry about 900 kg (1,900 lb) of gear. 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 edible konnyaku (devil's tongue) paste. Hungry workers stole the paste and ate it. Many workers were teen-aged girls, whose fingers were nimbler than any other 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. They had no idea of the purpose of their work. Large indoor spaces, such as sumo halls, sound stages, and theatres, were required for the envelope assembly.
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 and 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 towering flames. The Navy found balloons in the ocean. Balloon envelopes and apparatus were found in Montana, Arizona, Saskatchewan, in the Northwest Territories, and in the Yukon Territory. Eventually, an Army fighter managed to 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 January 1, 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 the balloons might be effective weapons.
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, the forests were generally too damp to catch fire easily or covered in snow.
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 U.S., 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. Working with Colonel Sidman Poole of U.S. 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, British Columbia, Manitoba, Alberta, Northwest Territories, Washington, 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 fighters destroyed fewer than 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.
Among the US units which fought the fire balloon was the 555th Parachute Infantry Battalion (United States).
|Killed near Bly, Oregon|
|1. Elsie Mitchell, age 26|
|2. Edward Engen, age 13|
|3. Jay Gifford, age 13|
|4. Joan Patzke, age 13|
|5. Dick Patzke, age 14|
|6. Sherman Shoemaker, age 11|
Japanese propaganda broadcasts announced great fires and an American public in panic, declaring casualties as high as 10,000. The press blackout in the U.S. was lifted after the deaths to ensure that the public was warned.
The balloon bombs were not very efficient, with a kill rate of 0.067%. General Kusaba's men launched over 9,000 balloons throughout the course of the project. The Japanese claim that they sent approximately 900 to America, although only about 300 have ever been found in America. Japanese estimates were 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 was large, and in the meantime the 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 March 10, 1945, one of the last paper balloons descended in the vicinity of the Manhattan Project's production facility at the Hanford Site. This balloon caused a short circuit in the powerlines supplying electricity for the nuclear reactor cooling pumps, but backup safety devices restored power almost immediately.