A recent Slashdot article, Japanese Balloon Battle, cites Slate‘s Censorship’s Trial Balloons – What happens when wartime news gets censored?, by Liam Callanan:
You’ve likely heard nothing about it. And that, of course, is the problem.
What have we likely heard nothing about? The Japanese Balloon Bombs of WWII. Except that I’ve heard plenty about the Japanese Balloon Bombs of WWII:
One of the best kept secrets of the war involved the Japanese balloon bomb offensive, prompted by the Doolittle raid on Tokyo on April 18, 1942 as a means of direct reprisal against the U.S. mainland. Some 9,000 balloons made of paper or rubberized silk and carrying anti-personnel and incendiary bombs were launched from Japan during a five-month period, to be carried by high altitude winds more than 6,000 miles eastward across the Pacific to North America. Perhaps a thousand of these reached this continent, but there were only about 285 reported incidents. Most were reported in the northwest U.S., but some balloons traveled as far east as Michigan.
The first operational launches took place on Nov. 3, 1944 and two days later a U.S. Navy patrol boat spotted a balloon floating on the water 66 miles southwest of San Pedro, California. As more sightings occurred, the government, with the cooperation of the news media, adopted a policy of silence to reduce the chance of panic among U.S. residents and to deny the Japanese any information on the success of the launches. Discouraged by the apparent failure of their effort, the Japanese halted their balloon attacks in April 1945.
The government changed its stance when a family of picknickers found a balloon bomb:
On May 5, 1945, six picnickers were killed in Oregon when a balloon bomb they dragged from the woods exploded. The U.S. Government quickly publicized the balloon bombs, warning people not to tamper with them. These were the only known fatalities occurring within the U.S. during WWII as a direct result of enemy action.
Fighters intercepted some of the balloons. Since they were 32 feet in diameter and held 19,000 cubic feet of hydrogen, I doubt they were hard to shoot down.
As some of the comments on Slashdot point out, what’s really fascinating about this is that the Japanese sent these balloons along the newly discovered Jet Stream. US experts traced the bombs back to Japan via the sand in the attached sandbags. It turned out to be unique to a particular beach in Japan — which US scientists knew by comparing the sand to samples from pre-war mineralogical surveys.