After the bombing of Pearl Harbor, America and its citizens were looking for ways to retaliate against the Japanese. One of those ways involved the creation of a ridiculous, yet perhaps a weirdly efficient bomb that would carry thousands of bats each tied with mini bombs that would set the Japanese houses on fire, destroying their property and hitting hard on their morale.

Called Project X-Ray, the United States developed experimental bat bombs to target Japanese cities during WWII. The idea was proposed by Dr. Lytle S Adams, a dentist and a friend of the then First Lady Eleanor Roosevelt, after Japan’s attack on Pearl Harbor.

Dr. Adams observed that since many of the Japanese buildings were made of bamboo, paper, and other inflammable materials, they are easy targets for incendiary fires. He submitted his idea to the White House in January 1942, and it was approved by President Roosevelt. The main targets for these bat bombs were going to be the industrial areas of Japanese cities. It was considered as a good plan since a large population of bats were available in New Mexico, namely Mexican Free-tailed Bats, and they are capable of carrying loads heavier than themselves.

The bat bombs contained numerous bats to which kerosene pills coupled with a fire triggering mechanism. After being dropped, the bomb would deploy a parachute at 1,000 feet and release the bats. The bats would fly off and find corners to roost, setting the house on fire.

The designing of these mini bombs was given to Dr. Louis Fieser, who also invented the military napalm (a flammable liquid), and came up with the idea of a lightweight pill made of nitrocellulose or gun-toting filled with kerosene that the bats could carry. To start the clock, the technicians would then inject copper chloride into the cartridge and tie it to the bat’s chest. When the bats reach a comfortable destination, they would gnaw at the string that holds the bomb to get rid of it, which would result in leaving the buildings with the chemically ticking bombs.

On May 15, 1943, armed bats were accidentally released and set fire to Carlsbad Army Airfield Auxiliary Air Base in New Mexico. The bomb trials were conducted over a mockup of a Japanese city built by Chemical Warfare Service in Utah.

The setback, however, didn’t discourage the Army. In August 1943, it was given to the Navy that named it Project X-Ray and was again passed on to Marine Corps in December. At Dugway Proving Grounds test site in Utah, what was called a “Japanese Village”, was built with a few Japanese houses to test the bat bombs, and were reconstructed for further testing when they took damage.

Strangely enough, the project was proving to be more efficient than normal bombs, because on a weight basis, the X-Ray could give 3,625 to 4,748 fires whereas the regular bombs could only give 167 to 400 fires.

According to the chief of incendiary testing at Dugway, in spite of their extremely small size, a reasonable number of destructive fires can be started using bat bombs. The advantage of X-Ray is that the fire watchers or the householders would be ignorant of any impending danger and the bombs can be placed within any building. They are also more effective because a bat bomb of equal weight as a normal bomb can set more than 10 times the number of fires set by the latter.

The project, however, was cancelled by Fleet Admiral Ernest J. King because it wasn’t likely to be ready for combat until 1945, and all resources were diverted to the development of atomic bombs which would later be deployed twice over Japan.

There were more tests to be conducted to perfect the X-Ray during the summer of 1944 and it was estimated that around $2 million were already spent on the project. Its developmental pace was thought to be too slow, and the allure and promised quick results of atomic bomb took precedence. This resulted in the project’s cancellation and diversion of resources. According to Dr. Adams, the bat bombs would have caused more devastation of property but with much less loss of life and without the aftereffects of an atomic bomb.

[sources: wikipedia, atlasobscura]