#23 - Balloon Bombs Delivered by the Jet Stream

Above: A map denoting Montana’s share of “Japan’s World War II Balloon Bomb Attacks on North America” in 1945, during the twilight months of World War II. Graphic by Stacey Schessler Osborne. CLICK HERE to access the Flathead Living article where this map appeared.

The Japanese knew . . .
During World War II, Japan released 9,300 balloon bombs that were intended to be carried to the United States by a high altitude wind known today as the "jet stream". Less than 400 of the bombs are known to have made the 6,000-mile journey. At least 35 of these bombs are known to have landed in Montana. At the start of the balloon-bomb program, which ran from November 1944 to April 1945, Americans were still unaware of Jet Streams. However Japan realized that these winds could transport the bomb-carrying balloons to the United States within days. Although the position and speed of the jet stream is variable, in the winter it often streaks across the Pacific from Japan to the United States. When inflated with hydrogen, each 33-ft. wide balloon could carry up to 794 lbs. of ballast and bombs. As they floated upward to a height of 4-8 miles they were taken into the jet stream and carried at speeds of up to 200 miles per hour toward the U.S.A. Little was known about the jet stream during WWII, but today meteorologists recognize the significance of these high altitude, high speed winds. Here are some jet stream facts.

1. There are other jet streams besides the one that carried balloon bombs across the Pacific. The one that carried the bombs (the same one that often blows over Montana) is called the sub-polar jet stream.

2. One of the most important aspects of the jet streams is that they influence the path of storms. Knowing where a jet stream is helps meteorologists predict the path of storms.

3. The first American to experience jet streams were crew members of the B-29 airplanes that bombed Japan during November 1944 because their airplanes could fly higher than the older B-17s.

4. The sub-polar jet stream typically marks the boundary between warmer air to the south and colder air to the north. In the summer of 1993, the jet stream stayed farther south than usual. This was an unseasonably cold, wet summer in Montana, and included historic flooding in the Midwest and snow in Butte, Montana on the 4th of July.

5. Twice daily (4 am and 4 pm MST) weather balloons (no bombs) are launched simultaneously from hundreds of sites including Great Falls and Glasgow in Montana. This effort lets the National Weather Service monitor the position and speed of the jet streams, and shows them how it has changed over the past 12 hours.

History of the balloon bomb effort . . .
As a result of the Japanese attack on Pearl Harbor (December 7, 1941), the United States sent airplanes to drop bombs on Tokyo in April of 1942. The bombing mission, known as the "Doolittle Raid", was dramatized in the 2001 blockbuster movie "Pearl Harbor." In response to the raid, Japan was compelled to strike American soil. The balloon bomb program was an attempt to accomplish this. The specific goal of balloon bomb effort, which ran from November 1944 to April 1945, was to start forest fires that would destroy property and divert manpower from the war effort. It was not successful. To find out how the bombs worked, and how the USA put an end to Japan's balloon bombing effort, CLICK HERE to watch this 15-minute YouTube video.

Term: jet stream