A little past six in the evening of 6 December, 1944, there was a curious sight over the small community of Thermopolis, Wyoming¹: a smallish unidentified flying object. Shortly after it was sighted the round object exploded, and a parachute floated down. A crater was found. What was it? Alien invasion or enemy action in an unlikely place?

Students of the history of aerial death and destruction, take note: the first-ever intercontinental weapons system was launched in 1944. By the Japanese. And the payload-carrying vehicles were made of paper.

Don't laugh. It could have been much deadlier than it turned out. As it was, the Japanese Fu-Go balloon bomb accounted for all six of the World War II fatalities that took place in the continental US². The Fu-Go, or fire balloon, was both a low-tech and a high-tech answer to the Japanese goal of bringing the war to North America. What did they hope to do? Set fire to Canadian and western US forests.

Thank Providence the jet stream flows strongest during the rainy season.

They Go Fu-Go

In late 1944, the war between the Allies and Japan was fierce and bitter. As the end to the European conflict hove in sight, more attention could be paid to the problem of containing the Japanese Empire. The Imperial Army and Navy wanted two things: revenge for the Doolittle Raids – airstrikes over the Japanese Home Islands – and a way to put the Canadians and Americans on the defensive. The problem? The US Navy owned most of the Pacific by now, hard-fought victory that this was, and the ocean was far too wide to reach across by plane. Rocket science was in its infancy, so the scientists of the Noborito Institute combined cutting-edge meteorological knowledge and technical know-how with a very ancient skill to create a new, potentially devastating, terror weapon: the fire balloon.

As part of climate research, Japanese scientists in the 1930s had discovered the existence of the jet stream: a strong flow of air at 30,000 feet, moving rapidly from west to east across the Pacific. The air stream was strongest in the winter months. The Noborito Institute found a military use for this information.

Japanese scientists constructed an ingenious bomb delivery system: hydrogen-filled balloons, 30 feet in diameter and 100 feet in circumference, made of sturdy washi paper. The paper was the low-tech part. The high-tech components were aneroid barometers, altimeters, and a complex firing mechanism that allowed the balloon to regulate its altitude and stay in the fast lane of the jet stream. If the balloon went too low, it dropped a couple of its paper-wrapped sandbags. If it went too high, it released some of its hydrogen. At just the right altitude, the Fu-Go raced along at 100 mph in the direction of enemy territory. This took 3-4 days. Once there, it dropped its payload, or so they hoped, ascended, and self-destructed. (Yes, there was a self-destruct mechanism.)

Wartime Fears and Group Action

The US military was worried about the fire bombs. They had no way of knowing this, but the Japanese had sent 9,000 of the potential fireballs wafting across the ocean between November 1944 and May 1945. The Noborito scientists estimated that about 10 percent would reach their target, and this appears to have been the case. Around 300 were sighted or recovered, with parts of many others picked up, including bits of washi paper in the streets of Los Angeles. The US and Canadian air forces shot down about 20 of them, but the fast-moving paper balloons were not easy targets. Fu-Go balloons were going off from the Pacific Northwest as far south as Mexico, and as far inland as Saskatchewan and Michigan. This was worrying.

What puzzled North Americans was how the balloons got there. At first, authorities suspected launches from submarines, beaches or even Japanese internment camps in the western US. A geologist from the US Geological Survey had the answer. 'Where's the sand from?' he asked. The sand in the balloons' ballast bags could be traced to the Japanese island of Honshu. Amazingly, these balloons were travelling between continents.

The incendiary devices on the balloons posed a threat to western forests, and Americans and Canadians were acutely aware of the dire manpower shortage when it came to fighting wildfires. Fortunately, the jet stream flowed best in the winter, when the Pacific Northwest tends to be drenched in rain or covered with heavy snowfall. The forest fires failed to materialise. More frightening was the possibility that the Noborito scientists would plant bioweapons – such as deadly anthrax – in their balloons. To everyone's relief, no sign of biological warfare was detected.

Locals who found the enemy balloons were thanked, and urgently requested not to discuss the matter. Newspapers co-operated in hushing up the balloon invasion. Information on captured balloons was marked 'Restricted'.

There is no record of how the Tokyo schoolgirls felt. The girls were recruited to assemble the large washi balloons, in spacious areas such as stadia and sumo gyms. The paper had to be glued together with konnyaku paste, a plant-based mucilage. Wartime hunger led the young workers to eat the paste.

War's Ironies

Keeping the balloons' effect a secret turned out to be a good decision, strategy-wise. When no reports of mass hysteria reached the Japanese, the Imperial Army decided that the programme had been a failure. They discontinued the effort. Had they gone on, things might have been different.

However, failing to inform the public of the dangers of the Fu-Go balloons had tragic consequences for a Klamath, Oregon, church outing. On 5 May, 1945, Mrs Mitchell and five of her 13- and 14-year-old Sunday School students stumbled upon a Fu-Go just as it exploded. Rev Mitchell, the teacher's husband, and a nearby construction crew were unable to save these six civilians – the only victims of enemy action in the continental US.

One of the last Fu-Go balloons had a close encounter with destiny: on 10 March, 1945, it descended near the Columbia River in Washington State. The balloon's explosion knocked out the power lines supplying electricity to the coolant tanks at the Hanford nuclear generator – part of the supersecret Manhattan Project. Back-up systems worked, and meltdown did not occur.

A few months after the cancellation of the Japanese low-tech attempt to bring fire down on western North America, US forces unleashed a higher-tech form of savagery on the Home Islands: the atomic bomb. The housing for this device wasn't made of washi paper.

By September, the war was over. Fire balloons ended up in museums, the nuclear arms race began, and clandestine US organisations immediately hired Noborito scientists to work for them³. Life went on, and people who saw flaming balloons in the sky breathed easier: they were either Chinese lanterns or UFOs, neither of which was likely to explode.

For Further Information

If you're interested in how the geologists figured out where the Fu-Go balloons were coming from, here's an excellent article by an expert: 'How Geologists Unraveled the Mystery of Japanese Vengeance Balloon Bombs in World War II', by J David Rogers of the Missouri University of Science and Technology.

Do you hunger after inside military intel? You may get more than you bargained for. Take a time-travel trip back to those days of yawning boredom as an officer with absolutely no narrative skills explains, in excruciating detail, exactly how a Fu-Go balloon gets across the Pacific Ocean and threatens the air force. Pay attention, there will be a test, soldier: 'Japanese Paper Balloon [Code name: Paper]', US Navy Training Film. (Restricted, but now declassified. Enjoy.)