Japan’s efforts to cause giant forest fires through the use of submarine-based floatplanes ceased after underwhelming effects. Another means was tried in November, 1944.
This time, the Japanese launched balloons from Japan to drift eastward on the prevailing winds. The balloons carried explosive and incendiary bombs to ignite forest fires and spread panic. In the ensuing months, over 9,000 balloons were launched, with at least 340 reaching the western United States and Canada.
The ingeniously-designed balloons varied in size, but many measured about 33 feet in diameter, and 70 feet from the top of the balloon to the payload at the bottom. The first ones were made of paraffined paper; later ones were fabricated silk and latex. Their payload consisted of four incendiary bombs and a 33-pound anti-personnel bomb.
The journey from Japan took three to five days at an altitude of about 35,000 feet, traveling at speeds between 80 and 120 miles per hour. As hydrogen gas bled from the balloons, the balloons descended in altitude. When they dropped below 25,000 feet, a barometric pressure switch would cause one of several sand-filled paper bags serving as ballast to be dropped, and the balloons rose back to 35,000 feet. This up and down flight carried the balloons across the Pacific Ocean.
By the time they reached the North American coast, they should have used up their supply of ballast sandbags. The bombs then became ballast, with one bomb dropping whenever the balloon dropped to 25,000 feet. When the bombs were depleted, a fuse ignited and destroyed the balloon in a bright fireball.
Witnesses saw some explode in the air. Other balloons were found on the ground, usually without bombs, but occasionally with bombs still attached. They traveled as far as Michigan and Texas. Most were sighted or found in British Columbia, Oregon, California, Washington, and Montana. Minor forest fires of unknown causes may have been started by the balloons in California and Oregon.
The first balloon was found in Montana in December, 1944. Analysis of the beach sand in the ballast bag determined it came from Japan. To avoid encouraging the Japanese to continue launching balloons, strict censorship was imposed. The balloons were not considered to a hazard to the public.
That changed on May 5, 1945. Reverend Archie Mitchell and his wife Elsie took five young teens on a picnic east of Bly, Oregon. While Mitchell parked the car, the others hiked into the woods. They called to him that they’d found something that looked like a balloon. He’d heard of the Japanese weapons, and shouted a warning not to touch it.
Too late. An explosion killed the six.
Censorship was lifted so the public could be informed of the existence of this hazard. More unexploded bombs were likely to be found in remote areas. The Japanese were unlikely to gain any advantage from the disclosure at this point. As it was later learned, the Japanese had scaled down and eventually discontinued using the balloons, considering them as ineffective as the floatplane-delivered bombs since they had heard of so few balloons reaching their target.
Mrs. Elsie Mitchell, 26, Edward Engen, 13, Jay Gifford, 13, Richard Patzke, 14, Joan Patzke, 13, and Sherman Shoemaker, 11, were the only American civilians killed in the continental United States during World War II.
Japanese school children had made many of the balloons. In 1987, several folded 1,000 paper cranes, a Japanese symbol of healing and peace, and sent them to the families of the slain picnickers. They wrote:
“We participated in the building of weapons used to kill people without understanding much beyond the knowledge that America was our adversary in a war. To think that the weapons we made took your lives as you were out on a picnic! We were overwhelmed with deep sorrow.”