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Bat Bomb Tests Go Awry

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Errant bats from the experimental Bat Bomb set the Army Air Base in Carlsbad, New Mexico on fire, 1942. United States Army Air Forces image.

Headlines for May 15, 1943, could have read, “Bat Bomb Destroys New Airfield,” but the plan to use small incendiary bombs attached to bats as a method to firebomb Japan was just as top secret as the Manhattan Project.

The idea to use bats as a way to deliver small fire-starting bombs was proposed by Dr. Lytle S. Adams of Pennsylvania. Dr. Adams was a dentist by trade, but dabbled in inventions as well as aviation. On December 7, 1941, Adams was vacationing in the southwestern United States. On this trip, he saw millions of bats emerging from the Carlsbad Caverns in New Mexico. He stated in a 1948 interview, “[I] 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 sent proposals for his project, and after some top level scientific review, President Roosevelt approved a plan to investigate the possible use of bat bombs on January 12, 1942.

The Adam’s Plan, as the proposal came to be known, called for millions of bats to be fitted with tiny incendiary bombs. The bats would then be dropped from a high altitude above Japanese industrial cities. Adams felt that a bat’s natural cold weather hibernation would be a beneficial element of the plan. Low temperatures at high altitudes would simulate winter hibernation, and as the bats fell they would gradually warm up and awaken. Once back to ground level, the bats would roost in places they felt most comfortable, such as eaves, attics, and other out of the way places. The tiny incendiary bombs would have a time delay start, and ignite as the bats were roosting. The small fires created would be hard to see, so they would be well established before anyone noticed them. This would make it harder for the fires to be put out once they were noticed, but would also give people a chance to flee unharmed. Adams felt that such a plan would cripple the manufacturing capabilities of Japan without causing extreme loss of life.

Once approval came from the White House, Dr. Adams set to work figuring out just how the bat bomb could work. The idea had two main components that had to work together, but were developed separately. Adams, along other naturalists, would work on the bat side of the equation. They would work closely with Thomas R. Taylor of the civilian group National Defense Research Committee (NDRC), who was appointed by President Roosevelt to oversee the scientific aspects of the project. Primarily, Taylor worked to design the bombshell which would carry the bats. Also part of NDRC was Dr. Louis Fieser, the inventor of napalm, who worked on the small incendiary bombs required to be carried by the bats.

Thomas Taylor at NDRC and Col. W.C. Kabrich of CWS began efforts to boost support for the program as well as develop an incendiary that would work for the bat bomb. By June 13, 1942, they had secured the support of the US Army Air Forces. In an official letter, Commanding General of the Army Air Forces Hap Arnold stated, “The Army Air Forces will cooperate with the Chemical Warfare Service when experiments reach the stage requiring tests from airplanes.” This support allowed both the bat and incendiary bomb teams to continue pursuing their various goals in developing a bat bomb. However, it seems that many upper level military leaders did not like the Adams Plan and were very doubtful of its practicality. Despite their reservations, work on the bat bomb continued, though both teams would be under immense pressure to produce positive results.

An early-model bat bombshell with mechanical opening device. Time Life Pictures/Getty Images

Once both the bat and the bomb teams had acquired the necessary information and tested their subjects separately, it was then time to test them together. The first tests were conducted in Muroc, California at the Army Air Force Base. Bats were gathered from Carlsbad and flown to Muroc. Bat unit member Jack Couffer constantly readjusted ice in the bat cages to ensure the bats did not overheat in the May heat of the Mojave Desert. These tests did not go well for the bat unit or those developing the incendiaries. The fire starting capabilities of the incendiary were not yet dependable, and the bomber pilot would not allow the bombs on board in case the igniters malfunctioned. This eventually led to Fieser’s development of safety pins attached to bottom of the trays. Also, the bat unit had to make due with a cardboard version of the bombshell they hoped to fabricate out of metal. However, the cardboard was too flimsy to hold up in the slipstream of the plane. Both teams went back to work with research and agreed to meet a month later. Lucky for those working on the Adams Plan, no high-ranking military officials attended the Muroc tests.

The next tests took place in Carlsbad, New Mexico about six weeks after the Muroc tests. Unlike Muroc, these tests were attended by an Army Air Forces captain and a CWS colonel. USMC General Louis DeHaven also attended the testing, having been notified of them by US Navy Admiral Ernest King. The location was great for the bat team, as it was close to a bat colony.  It was also the location of the Carlsbad Air Force Base. Due to the top secret nature of the Adams Plan, the team was allowed to use a newly constructed, but not yet occupied, auxiliary air field on the base. The new air field was complete with barracks, offices, hangars, a control tower, and several other buildings.

In the six weeks since the Muroc tests, Dr. Fieser did not have time to make all of the needed adjustments. The new mechanical time delay igniter was not ready, nor was the safety pin mechanism. The team was forced to use a chemical delay igniter and bombs with no safety mechanism. These bombs were fine for testing fire starting abilities on the ground, but they were not stable enough to load on the airplane. Doing so could endanger the plane, the crew and the surrounding area. However, they overcame this obstacle by informing the brass that sending armed bats out over the airfield and the area was not a good idea. Since armed bats could potentially set homes and other structures on fire. Therefore, bats released from the plane needed to have dummy bombs attached to them anyway.

The first trails at Carlsbad tested the effectiveness of the bombshell. The shell was dropped loaded with bats strapped with dummy bombs. The chute deployed as intended, and the bat trays came out of the shell accordion style. Soon, the tiny bats began to launch off the trays in all directions. This part of the test was a success. The team spent hours combing the area to try to find all the places the bats had flown to. They found them roosting in eaves and barns miles from the drop zone, another success for the bat team. A second bomb was loaded and deployed with similar results.

Unfortunately, though the team suffered a serious setback at these tests. Fieser, in an effort to make a training film, wanted to put live bombs on the bats to demonstrate the incendiaries igniting. The idea was that the bats would be cooled down to a semitorpid state, and the bombs would be attached and activated with the chemical delay igniter before the bats awoke. Thus, the incendiaries would ignite while the bats were on the table. This way the film crew could photograph every aspect of the Adam’s Plan right in front of them. Unfortunately for the team, the heat of the day warmed more quickly than expected and only kept them “hibernating” for about ten minutes. Fieser had set the timers for fifteen minutes. As the armed bats awoke, they took flight. Before the bats could be caught, they followed the Adams Plan perfectly, roosting in the eaves of the airfield’s buildings. Everything worked as it was supposed to, the bats and incendiaries worked perfectly. The setback however was that the newly built, unoccupied airfield burned to the ground. Due to the top secret nature of the Adams Plan fire crews were not even allowed in to try and salvage some of the buildings in order to prevent them from seeing how the fires had started. It took only six bats to burn the Carlsbad auxiliary air field.

The bat bomb would continue to be tested for almost another year. Ultimately though, in February 1944, despite continued progress by Fieser and the bat unit, Project X-Ray was discontinued. Several factors were cited for the project’s cancelation. First, some felt that the fundamental idea of the plan was flawed, and that reliable data could not be obtained. Second, there were still many uncertainties regarding the bat’s behavior. Furthermore, the team knew all along that the bats’ natural rhythm meant that they could only launch this type of attack seasonally. The bats lived in Mexico in the winter months, and were not strong enough in the spring months to carry the seventeen-gram incendiary. Despite the project’s pace, it would not have been ready until mid-1945, a full year from when the plan was terminated. Finally, the US military had already spent close to two million dollars on the project, and was not pleased with the time frame still needed to complete the project and thus a continued financial investment would be necessary. Additional, even though the atomic bomb is not cited anywhere as a cause for discontinuing the bat bomb project, many involved with the Adams Plan believe another top secret bomb being developed under the codename the Manhattan Project was thought to have more potential.

This post by Toni Kiser, Assistant Director of Collections & Exhibits/Registrar and co-author of Loyal Forces: The American Animals of WWII.


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