For most of World War II, the United States military was seriously developing a plan that would have unleashed thousands of firebomb-armed bats from planes above Japanese cities. And it could have worked, as Cara Giamio writes for Atlas Obscura.
An American dentist named Lytle S. Adams had bats on the brain, Giamio reports. When the Japanese navy attacked Pearl Harbor on December 7, 1941, Adams had just back from a vacation that included a trip to Carlsbad Cavern — and he was struck by the millions of Mexican Free-Tailed bats that roost in the caves.
Like many Americans, Adams was enraged by the Pearl Harbor attack and quickly drafted a plan to strap miniature bombs to bats and drop them over Japanese cities. At the time, the stereotypical image of Japanese buildings was of many wood-and-paper houses packed together closely. Adams imagined that the bats would stream out of bombers and instinctively flock to the rooftops and eaves of these buildings. When the timers on the bombs attached to each bat would run down, the destruction would cascade across entire neighborhoods and cities, terrorizing the populace.
With a little help from his friend, Eleanor Roosevelt, Adams’ plan eventually made it to the desks of President Franklin D. Roosevelt and his top military brass. Roosevelt thought it was “a perfectly wild idea but is worth looking into” and gathered a crack team of military experts and scientists to develop bombs small enough to execute Adams’ plan, Giamio writes. It was called “Project X-Ray.”
But as Adams and his team worked on their tiny firebombs, the Japanese military was busy with their own crazy scheme: the fu-go. In the 1920’s, a Japanese scientist named Wasaburo Oishi discovered the jet stream, and the Japanese military believes they could use it to conduct their own terror campaign against the United States, Linton Weeks reports for NPR. The fu-go plan "called for sending bomb-carrying balloons from Japan to set fire to the vast forests of America, in particular those of the Pacific Northwest. It was hoped that the fires would create havoc, dampen American morale and disrupt the U.S. war effort," James M. Powles writes for the journal World War II.
The balloon bombs were about 33 feet in diameter and made of a traditional Japanese paper called “washi.” Each fu-go carried an elaborate canopy of firebombs and sandbags, which were timed to drop off and keep the balloon drifting through the jet stream, David Kravets writes for Wired.
Project X-Ray was eventually canceled in 1944, but not because it didn’t work — in fact, early tests of the bat bombs showed that they could have been very effective. But the military decided to funnel all available funding into developing atomic weapons with the Manhattan Project and the bat bombs were given the boot. The fu-go, on the other had, were actually used and resulted in several casualties on the American mainland. However, after early reports of the bombs reached the U.S. military, it was covered up to stop the Japanese from finding out that their plan was working, Radiolab reports.
While most of the 6,000 or so balloon bombs the Japanese launched never reached the mainland, some may still be out there — and have been found by hikers as recently as 2014. If you’re hiking through the Pacific Northwest and come across a strange paper lantern, it might be best to leave it be.