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No. 1091:
Balloon Bombs

Today, a tale of two secret weapons. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

The late days of WW-II finally brought the war to my quiet home in Minnesota. Since Tokyo was over 6000 miles away, our mutual slaughter had largely been carried out in the Pacific Ocean. Then, in January, 1945, we learned about Japan's secret weapon. She was trying to ignite our mainland with incendiary bombs.

The bombs drifted over North America, carried by 30-foot-diameter balloons. They were made of fine Japanese mulberry paper called washi. The bomb was mounted on a horizontal ring below the balloon, along with a complex array of small sandbags.

The hydrogen expanded by day, and the balloon rose until a sensor detected that it was too high. Then it vented some hydrogen. As the balloon shrank by night it fell until another sensor dropped sandbags. Finally, after three such cycles, the sensor lit a long fuse and vented the remaining hydrogen. The balloon then landed on American soil, and, soon after, it exploded.

At first we thought these bombs were being released by submarines off the West Coast. But the balloons were too big and far too numerous. They would've taken too many submarines!

Once we'd found a few sandbags, the Geological Survey set out to learn where the sand came from. Sand carries a distinct fingerprint of minerals, occasional coral fragments, and fossilized diatoms. (A diatom is the kind of single-celled creature that makes up algae.) Geological detective work soon pinned down a region near Tokyo. The bombs were making an astonishing journey all the way from Japan -- something no one had thought possible.

We didn't know that Japanese meteorologists had discovered a jet stream, moving very fast at altitudes over 30,000 feet. The balloons rode that jet stream and got here in a scant three days.

So bombs fell harmlessly near Klamath Falls, Oregon, and Bigelow, Kansas. They fell in remote corners of Manitoba, Colorado, Texas, and Mexico. They reached Iowa, North Dakota -- even Michigan. None landed in St. Paul. But, Oh, Father Christmas! How this 14-year-old boy longed to see one. Meanwhile the Japanese press said panic was gripping America, which was now in flames.

Forensic geologist John McPhee tells the story of this byroad in military history. It seems that only one balloon bomb actually killed anyone. It landed in the Cascade mountains. Five Sunday-school children and their minister's wife, all on a fishing trip, found it just before it exploded. It killed all six.

But I said this was a tale of two secret weapons. Another balloon bomb ran into an electric line at the Hanford plant in Washington and cut the power. For a while, it shut down the production of plutonium for the atom bomb that would fall on Nagasaki -- only five months later.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

McPhee, J., Balloons of War. The New Yorker, January 29. 1996, pp. 52-60. I am grateful to Margaret Culbertson, UH Art and Architecture Library, for suggesting the episode and providing me with McPhee's article.