Japanese Begin Release of Incendiary Balloons to Spread Terror in America

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Japanese Begin Release of Incendiary Balloons to Spread Terror in America

Line drawing of a balloon bomb
Image courtesy of http://chicagoboyz.net/archives/41791.html
(Unless otherwise indicated, all illustrations are courtesy of Wikipedia)

Today in Military History: November, 3, 1944

Our spotlight on military history for today falls upon the latter months of the Second World War, and the shrinking Japanese "Greater East Asian Co-Prosperity Sphere." Trying to find some way to take the war to the Americas, the Japanese military devised long-distance fire balloon attacks that made nary a dent in the American war effort. It was also largely hushed up until after the war ended.


By the summer of 1944, American military forces in the Pacific had pushed Japanese forces back from the Solomon Islands, the Gilbert and Marshall islands, and the Mariana and Palau islands. The naval battles of the Coral Sea, Midway, and the Philippine Sea had established U.S. naval supremacy. As a result, the Japanese war ministry sought out projects to bring the war to the American homeland.

The concept for the was the brainchild of the Imperial Japanese Army's 's Ninth Army's Number Nine 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 reportedly blew at altitudes above 30,000 feet and could carry a large balloon across the Pacific in three days, over a distance of more than 5000 miles. 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.

Making a Fūsen Bakudan (Balloon Bomb)

A hydrogen balloon expands when warmed by 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 30,000 feet, 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 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. By that time, it was likely over the North American continent, and its ballast was expended. A final flash of gunpowder released the bombs, also carried on the wheel, and lit a 64-foot 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 1000 pounds of gear. At first the balloons were made of conventional rubberized silk. Shortly after the first balloons were produced, an order went out for ten thousand balloons made of washi, a paper derived from mulberry bushes that was leak-proof 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 – though hungry workers stealing the paste for food created some problems. Many workers were nimble-fingered teenaged school girls. They assembled the paper in many parts of Japan. Large indoor spaces, such as sumo halls, sound stages, and theatres, were required for the envelope assembly.

Fire balloon shot down by a Navy aircraft on January 10, 1945,
Re-inflated and tested at Moffett Field, CA, U.S. Army photograph

The bombs most commonly carried on the balloons were:

  • Type 92 33-pound high-explosive bomb consisting of 9.5 pounds of picric acid or TNT surrounded by 26 steel rings within a steel casing 4 inches in diameter and 14.5 inches long and welded to an 11-inch tail fin assembly;
  • Type 97 26-pound thermite incendiary bomb using the Type 92 bomb casing and fin assembly containing 11 ounces of gunpowder and three 3.3-pound magnesium containers of thermite; or,
  • 11-pound thermite incendiary bomb consisting of a 3.75-inch steel tube 15.75 inches long containing thermite with an ignition charge of magnesium, potassium nitrate, and barium peroxide.

Each balloon was about 33 feet in diameter, and when fully inflated contained 19,000 cubic feet of hydrogen.

Coming to America…

The first balloon was released on November 3, 1944. The first few balloons carried atmospheric equipment, so that Japanese direction finding stations could track their progress. When the program was finally shut down, more than 9000 balloon bombs had been launched.

The Japanese chose to launch the campaign in November; because the period of maximum jet stream velocity is November through March. This limited the chance of the incendiary bombs causing forest fires, as that time of year produces the maximum North American Pacific coastal precipitation, and forests were generally snow-covered or too damp to catch fire easily. On November 4, 1944 a United States Navy patrol craft discovered one of the first balloons floating off San Pedro, Los Angeles. National and state agencies were placed on heightened alert status when balloons were found in Wyoming and Montana before the end of November.

Locations of sightings or recovery of balloon bombs against North America; Image courtesy of http://news.nationalgeographic.com/news/2013/05/130527-map-video-balloon-bomb-wwii-japanese-air-current-jet-stream
Locations of sightings or recovery of balloon bombs against North America
Image courtesy of http://news.nationalgeographic.com/news/2013/05/130527-map-video-balloon-bomb-wwii-japanese-air-current-jet-stream/

The balloons continued to arrive in Oregon, Kansas, Iowa, British Columbia, Saskatchewan, Manitoba, Alberta, the Yukon, Northwest Territories, Washington, Idaho, South Dakota and Nevada. In Nevada, one balloon bomb landed near Yerington that was discovered by cowboys who cut it up and used it as a hay tarp. Another was discovered by a prospector near Elko who delivered it to local authorities on the back of a donkey, and another was shot down by U.S. Army Air Forces planes near Reno. Military fighters tried on numerous occasions to shoot down these weapons, but they flew very high and fast. Only about 20 of the balloons were taken out.

Fearing the possibility of wildfires in the Pacific Northwest, the Fourth Air Force, Western Defense Command and Ninth Service Command organized the Firefly Project of 2,700 troops including 200 paratroopers of the 555th Parachute Infantry Battalion with. These men were stationed at critical points for use in fire-fighting missions. The 555th suffered one fatality and 22 injuries fighting fires.

As more and more sightings occurred, the War Department, the FBI, and the Office of Censorship clamped a tight lid on the circulation of news stories about these mysterious balloons. The number of reported balloon incidents topped 300 by the time the war ended. Though most of them came down in the Pacific Northwest with 45 in Oregon, 28 in Washington, 57 in British Columbia, and 37 in Alaska, many others were driven greater distances by the jet stream. One balloon fell on a farm in Kansas, and two were discovered as far south and east as Texas. Another balloon bomb landed near Powell, Wyoming; it was only a few miles from landing right in the middle of the Heart Mountain Japanese Relocation Camp.

Balloon Bomb Claims Six Victims: Saturday, May 5, 1945

Near Bly, Oregon, local pastor Archie Mitchell of the Bly Christian and Missionary Alliance Church, his pregnant woman Elsie Winters Mitchell, and five children from their Sunday school class (ages 11-14) drove through the forest near Gearhart Mountain looking for a good place for a picnic and to do some fishing. They had to stop at this spot due to construction and a road closing.

[The parents of the five children were locals who were working overtime for the war effort, even though the Second World War was winding down. The Rev. and Mrs. Mitchell wanted to give these children some semblance of a normal home life.]

Elsie and the children got out of the car, while Rev. Mitchell drove on to find a parking spot and to unload the equipment. As Elsie and the children looked for a good picnic spot, they saw a strange balloon lying on the ground. By this time, Rev. Mitchell was approaching the group, when his wife said, "Look what we found. It's a balloon." Apparently, Archie had heard about the Japanese balloon bombs. As he shouted a warning, there were two explosions; the children were killed immediately, and Elsie died as Archie used his hands to extinguish the fire on her clothing. These are the only known deaths caused by the balloon bombs.

Military personnel arrived on the scene within hours, and saw that the balloon still had snow underneath it, while the surrounding area did not. They concluded that the balloon bomb had drifted to the ground several weeks earlier, and had lain there undisturbed until found by the group.

In 1950 a monument was dedicated to the memory of the six people killed by the balloon bomb. It located in the Fremont-Winema National Forests, Lake County OR. Originally owned by the Weyerhauser Company, in 1996 the monument and land was donated to the Forest Service, Department of Agriculture. It is also on the National Register of Historic Places. Several Japanese civilians have visited the monument to offer their apologies for the deaths that took place here, and several cherry trees have been planted around the monument as a symbol of peace.

Mitchell Monument, Fremont-Winema National Forests, Lake County OR; Site of only civilian casualties in U.S. from enemy action during World War II
Mitchell Monument, Fremont-Winema National Forests, Lake County OR
Site of only civilian casualties in U.S. from enemy action during World War II


Because of the news blackout about balloon bomb sighting, the Imperial Japanese government had no evidence of any effect, and consequently gave the order to cease funding the balloon bomb operations in April 1945, believing that the mission had been a total failure. The program's expense was large, and in addition B-29 raids had destroyed two of the three hydrogen plants needed by the project. Disruption of railroad lines needed to transport the materials needed for bomb construction also likely played a role. The last balloon bombs were launched later that month.

Footnote #1: In Washington, a balloon bomb nearly had the strategic effect the Japanese where hoping for when one blew up dangerously close to the Hanford facility where the U.S. was making plutonium for nuclear bombs. The balloon struck power lines north of the facility and knocked out power temporarily, but back-up generators kicked in within minutes – it was the only wartime industrial facility shut down due to enemy action.

Footnote #2: About 300-350 of the fire bombs landed in the U.S. and Canada, but local conditions or mechanical failure kept them from detonating. Below is a photo of one device currently on display at the National Museum of the U.S. Air Force at Wright-Patterson Air Force Base near Dayton, OH.

Recovered balloon bomb – balloon, steel casing, and wiring; On display at the National Museum of the U.S. Air Force, Dayton OH; Image courtesy of https://bbs.stardestroyer.net/viewtopic.php?t=125456
Recovered balloon bomb – balloon, steel casing, and wiring;
On display at the National Museum of the U.S. Air Force, Dayton OH
Image courtesy of https://bbs.stardestroyer.net/viewtopic.php?t=125456

Footnote #3: The Japanese Imperial Army Noborito Institute cultivated anthrax and yersinia pestis (bubonic plague) strains. Furthermore, it produced 20 tons of cowpox viruses. There was a proposal to deploy some of these biological weapon on fire balloons. However, this possible biological warfare was not realized.

Footnote #4: In October of 2014, a pair of loggers in Lumby, British Columbia, found the remnants of a balloon bomb. After contacting Canadian authorities, a Royal Canadian Navy ordinance disposal team destroyed the relic in a controlled explosion. [Even though it is 70+ years since these balloon bombs were launched, they are still considered "armed and dangerous."]

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