Bat bombs were tiny incendiary bombs attached to bats that the United States developed during World War II with the hope of attacking mainland Japan. Four biological factors gave promise to this plan. First, bats occur in large numbers (four of the caves in Texas are each occupied by several million bats). Second, bats can carry more than their weight in flight (females carry their young — sometimes twins). Third, bats hibernate, and while dormant, they do not require food or complicated maintenance. Fourth, bats fly in darkness and then find secretive places (such as flammable buildings) to hide in daylight.

The plan was to release bomb-laden bats at night over Japanese industrial targets. The flying bats would disperse widely, then at dawn, they would hide in buildings. Shortly thereafter, built-in timers would ignite the bombs, causing widespread fires and chaos. The bat bomb idea was conceived by dental surgeon Lytle S. Adams, who submitted it to the White House in January 1942, where President Roosevelt subsequently approved it. Adams was recruited to research and obtain a suitable supply of bats.

Project details
By March of 1943, a suitable species had been selected. The project was considered severe enough that Louis Fieser, the inventor of military napalm, designed 0.6 ounces (17 g) and one-ounce (28 g) incendiary devices to be carried by the bats. A bat carrier looking like a bomb casing was designed that included 26 stacked trays, each containing compartments for 40 bats. The airlines would be dropped from 5000 feet (1525 m). Then, the trays would separate but remain connected to a parachute that would deploy at 1000 feet (305 m). It was envisioned that ten B-24 bombers flying from Alaska, each carrying a hundred shells packed with bomb-carrying bats, could release a million bat bombs over the target — the industrial cities of Osaka Bay. A series of tests to answer various operational questions were conducted. In one incident, the Auxiliary Army Air Base in Carlsbad, New Mexico, was set on fire when armed bats were accidentally released. The bats incinerated the test range and made roost under a fuel tank. Following this setback, the project was relegated to the Navy in August 1943, who renamed it Project X-Ray and then passed it off to the Marine Corps that December. The Marine Corps moved operations to the Marine Corps Air Station at El Centro, California. After several experiments and operational adjustments, the definitive test was carried out on a mockup of a Japanese city built by the Chemical Warfare Service at their Dugway Proving Grounds test site in Utah.

Observers at this test produced optimistic accounts. The chief of incendiary testing at Dugway wrote: “A reasonable number of destructive fires can be started despite the tiny size of the units. The main advantage of the units would seem to be their placement within the enemy structures without the knowledge of the householder or fire watchers, thus allowing the fire to establish itself before being discovered.” The NDRC (National Defense Research Committee) observed, “It was concluded that X-Ray is an effective weapon.” The Chief Chemist’s report stated that on a weight basis, X-ray was more effective than the standard incendiary bombs used at the time. “Expressed in another way, the regular bombs would give probably 167 to 400 fires per bomb[er] load where X-Ray would give 3625 to 4748 fires.”

More tests were scheduled for the summer of 1944, but the program was canceled by Fleet Admiral Ernest J. King when he heard that it would likely be combat-ready in mid-1945. By then, it was estimated that $2 million had been spent on the project. It is thought that the development of the bat bomb was moving too slowly and was beaten out of the race for a quick end to the war by the Atomic Bomb project.

Dr. Adams maintained that the bat bombs would have been effective without the devastating effects of the Atomic bomb. He is quoted as having said:

“ Think of thousands of fires breaking out simultaneously over a circle of forty miles in diameter for every bomb dropped.
Japan could have been devastated, yet with slight loss of life.[1]

Here is the original Article by C. V. Glines

Illustrations by Chris Fauver

DR. Lytle S. Adams, a dental surgeon from Irwin, Pa., was vacationing in the southwestern US on December 7, 1941. Like millions of Americans, he was shocked at the news from Pearl Harbor and couldn’t believe Japan had been able to mount such an attack. In those days, “Made in Japan” meant cheap, shabby, and inferior. Americans’ image of Japan was of crowded cities filled with paper-and-wood houses and factories.

Dr. Adams pondered how the US could fight back. In a 1948 interview with the Bulletin of the National Speleological Society, Dr. Adams recalled: “I had just been to Carlsbad Caverns, N. M., and had been tremendously impressed by the bat flight. . . . Couldn’t those millions of bats be fitted with incendiary bombs and dropped from planes? What could be more devastating than such a firebomb attack?”

Dr. Adams went back to Carlsbad and captured some bats. At home, he read everything he could find about the tiny flyers. He learned that there are nearly 1,000 species worldwide and that each bat lives up to thirty years. The most common bat in North America is the free-tailed, or guano, bat, a small brown mammal that may catch more than 1,000 mosquitoes or gnat-sized insects–a load twelve times its size–in a single night. Weighing about nine grams, it can carry an external load of nearly three times its weight.

On January 12, 1942, Dr. Adams sent a proposal to the White House to investigate the possible use of bats as bombers. In those days, well-meaning citizens were proposing all kinds of warfare ideas, most impractical. However, after being sifted through a top-level scientific review, this idea became one of the very few given the green light. It was passed to the Army Chemical Warfare Service (CWS) for further inquiry in conjunction with the Army Air Forces. The official CWS history states simply: “President Roosevelt OK’d it, and the project was on.”

Dr. Adams and a team of field naturalists from the Hancock Foundation, University of California, immediately set to work and visited several likely sites where bats would be available in large quantities. Bats are found chiefly in caves, though great numbers roost in attics, barns, houses, bridges, and piles of rubbish. “We visited a thousand caves and three thousand mines,” Dr. Adams later related. “Speed was so imperative that we generally drove all day and night when we weren’t exploring caves. We slept in the cars, taking turns driving. One car in our search team covered 350,000 miles.”

A Choice of Bats

The most giant bat found was the mastiff, which had a twenty-inch wingspan and could carry a one-pound stick of dynamite. However, the team discovered that more numbers needed to be available. The more common mule-eared, or pallid, bat could carry three ounces, but naturalists determined it needed to be more challenging for the project.

Finally, the team selected the free-tailed bat. Though it weighed only one-third of an ounce, it could fly well with a one-ounce bomb. The largest colony of free-tailed bats found by Dr. Adams’ naturalists, some twenty to thirty million, was in Ney Cave near Bandera, Tex. The colony was so large, according to a report by CWS Capt. Wiley W. Carr states, “five hours is required for these animals to leave the cave while flying out in a dense stream fifteen feet in diameter and so closely packed they can barely fly.”

The collection of the bats was relatively easy. Three nets, about three feet in diameter, on ten-foot poles, were passed back and forth across the cave entrance as the bats flew out. As many as 100 could be caught on three passes. They were removed from the nets and placed in cages in a refrigeration truck. Dr. Adams took some to Washington, releasing them in the War Department building to show Army officials how they could each carry a dummy bomb.

In March 1943, Hq had the authority to proceed with the experiment. USAAF. Subject: “Test of Method to Scatter Incendiaries.” Purpose: “Determine the feasibility of using bats to carry small incendiary bombs into enemy targets.”

The bats’ habits were studied intently. Meanwhile, Dr. L. F. Fisser, a special investigator for the National Defense Research Committee, began to design bombs light enough to be carried by bats. He did not find it difficult because there was a precedent for miniature incendiaries. England’s principal firebombs, used in World War I, were called “baby incendiaries.” Filled with a unique thermite mixture, these bombs weighed 6.4 ounces each.

Arming the Bats

Dr. Fisser designed two sizes of incendiary bombs for the bomber-bat experiments. One weighed seventeen grams and would bum for four minutes with a ten-inch flame. The other weighed twenty-eight grams and would burn for six minutes with a twelve-inch flame. They were oblong, nitrocellulose cases filled with thickened kerosene. A small time-delay igniter was cemented to the case along one side.

The time-delay igniter consisted of a tightened firing pin against a spring by a thin steel wire. When the bombs were ready, a copper chloride solution was injected into the cavity through which the steel wire passed. The copper chloride would corrode the wire; when the wire was completely corroded, the firing pin snapped forward, striking the igniter head and lighting the kerosene. Small time-delay smoke bombs were also designed so ground observers could trace test flights of bats. They burned for thirty minutes with a yellowish flame that could be seen several hundred yards away at night; white smoke was also emitted.

To load a bomb aboard a bat, technicians attached the case to the loose skin on the bat’s chest with a surgical clip and a piece of string. Groups of 180 were released from a cardboard container that opened automatically in midair at about 1,000 feet, after which, according to the CWS history, “bats were supposed to fly into hiding in dwelling and other structures, gnaw through the string, and leave the bombs behind.”

In May 1943, about 3,500 bats were collected at Carlsbad Caverns, flown to Muroc Lake, Calif., and placed in refrigerators to force them to hibernate. On May 21, 1943, five drops with bats outfitted with dummy bombs were made from a B-25 flying at 5,000 feet. The tests were unsuccessful; most of the bats, not fully recovered from hibernation, did not fly and died on impact. The bat-bomber research team was transferred a few days later to an Army Air Forces auxiliary airfield at Carlsbad, N. M.

Newly recruited bats were placed in ice cube trays and cooled to force them into hibernation. They were then transported to the airfield to await test mission assignments. Captain Carr explains how the test cartons were prepared for the drop tests: “Bats were taken from the refrigeration truck in a hibernated state in lots of approximately fifty. A biologist took them individually, and about a half inch of loose chest skin was pinched away from the flesh. While this operation was being done, another group was preparing the torches. One operator injected the solution in the delay [mechanism], another sealed the hole with wax, and another placed the surgical clip that was fastened to the torch by a short string. . . . The incendiary was then handed to a trained helper who fastened it to the chest skin of the bat.” Drops were made from a North American B-25 and a Piper L-4 Cub.

Complications Arise

There were many complications. Many bats didn’t wake up in time for the drops. The cardboard cartons did not function properly, and the surgical clips proved challenging to attach to the bats without tearing the delicate skin. When these problems were resolved, new bats were taken up for drop tests with dummy bombs attached. Many took advantage of their freedom to escape or refused to cooperate and plummeted to earth.

The Army tests were called off on May 29, 1943, and Captain Carr prepared a final report. “The bats used at Carlsbad weighed an average of nine grams,” he wrote. They could carry eleven grams without trouble and eighteen grams satisfactorily, but twenty-two grams appeared excessive. The ones released with twenty-two-gram dummies didn’t fly very far, and three returned to the building where we were working in a few minutes. One flew underneath, landed on the roof, and attached itself to the wall. The ones with eleven-gram dummies flew out of sight. The next day, an examination of the grounds around a ranch house about two miles from the point of release disclosed two dummies inside the porch, one beside the house, and one inside the barn.”

More than 6,000 bats were used in the Army experiments. In his secret report, dated June 8, 1943, Captain Carr concluded that a better time-delay parachute-type container, new clips, and a simplified time-delay igniter should be designed if further tests were to be carried out. He also recommended a six-week controlled study of bats during artificial hibernation. After this, he said, another test should be conducted with 5,000 bats.

Captain Carr reported tersely that “testing was concluded . . . when a fire destroyed a large portion of the test material.” He did not mention that, in one test, a village simulating Japanese structures burned to the ground. Nor did he state that a careless handler had left a door open, and some bats escaped with live incendiaries aboard and set fire to a hangar and a general’s car. Records do not reflect the general’s reaction, but he could not have been pleased. Shortly after that, in August 1943, the Army passed the project to the Navy, renamed Project X-Ray.

The Sea Services Take Over

In October 1943, the Navy leased four caves in Texas and assigned Marines to guard them. Dr. Adams designed screened enclosures that were prefabricated at Hondo Army Air Field and placed over the cave entrances to capture the bats. If necessary, a million could be collected in one night. By then, the Navy had handed the project off to the Marine Corps.

The first Marine Corps bomber-bat experiments began on December 13, 1943. In subsequent tests, thirty fires were started. Twenty-two went out, but according to Robert Sherrod’s History of Marine Corps Aviation in World War II, “four of them would have required the services of professional firefighters. A new and more powerful incendiary was ordered.”

Full-scale bomber-bat tests were planned for August 1944. However, when Fleet Admiral Ernest J. King, Chief of Naval Operations, found that the bats would be combat-ready in mid-1945, he abruptly canceled the operation. By that time, Project X-Ray had cost an estimated $2 million.

Dr. Adams was disappointed. He maintained that fires generated by bomber bats could have been more destructive than the atomic bombs that leveled Hiroshima and Nagasaki and ended the war. He found that bats scattered up to twenty miles from their release. “Think of thousands of fires breaking out simultaneously over a circle of forty miles in diameter for every bomb dropped,” he said. “Japan could have been devastated, yet with small loss of life.”

October 1990, Vol. 73, No. 10 
Copyright Air Force Association. All rights reserved

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