To attach the bomb to a bat, technicians clipped the case to the loose skin on the bat’s chest with a surgical clip and a piece of string. The bats were dropped from a plane in a cardboard container that would open in midair at about 1,000 feet. According to one CWS report, the bats were then expected ‘to fly into hiding in dwellings or other structures, gnaw through the string, and leave the bombs behind.’

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In early May 1943, about 3,500 bats were collected at Carlsbad Caverns and flown in a North American B-25 that had been assigned to the project to Muroc Dry Lake, Calif., for tests. The bats were placed in refrigerators and forced to hibernate. On May 21, 1943, five boxes of bats were dropped from 5,000 feet, but the test was unsuccessful because the bats, not fully recovered from hibernation, could not fly.

The project was transferred to an auxiliary field under construction at Carlsbad, and secret tests continued. This time bats were placed in ice cube trays and cooled off to place them in hibernation. They were then positioned in cardboard cartons for the drop tests. Captain Carr explained the procedure: ‘Bats were taken from the refrigeration truck in a hibernated state in lots of approximately fifty. They were taken individually by a biologist, and about a one-half inch of loose chest skin was pinched away from the flesh. While this operation was being done, another group was preparing the incendiaries. 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 incendiary by a short string….The incendiary was then handed to a trained helper who fastened it to the chest of the bat.’

Drops of the bats were made with dummy bombs from a B-25 and a Piper L-4 Cub, but troubles once again developed. Many of the bats didn’t awaken from hibernation in time to be able to fly, the cardboard cartons didn’t always open properly, and the surgical clips proved difficult to attach to the chests of the bats. Team members worked to resolve these problems, and more bats were secured. This time, however, they woke up too quickly when they were released, then escaped.

Captain Carr stated in an interim report: ‘The bats used at Carlsbad weighed an average of nine grams. They could carry eleven grams without any trouble and eighteen grams satisfactorily, but twenty-two grams appeared to be excessive. These didn’t fly very far, and three returned in a few minutes to the building where we were working. One flew underneath, one landed on the roof, and one 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 away from the point of release disclosed two dummies inside the porch, one beside the house, and one inside the barn.’

Tests continued, and more than 6,000 bats were used in the experiments. In a report dated June 8, 1943, Carr stated that if further tests were to be carried out, a better time-delay parachute-type container, new clips and a simplified time-delay igniter should be designed. He added that ‘testing was concluded…when a fire destroyed a large portion of the test material.’ What he didn’t point out was that a barracks, a control tower and other buildings at the Carlsbad auxiliary field had been set afire by the bats on the not-yet-occupied base.

The Army had had enough of the experiment by August 1943, and the project was passed to the Navy and assigned to the Marine Corps as Project X-Ray. Marines were assigned to guard four bat caves in Texas, and their first tests began on December 13, 1943. Experiments were carried out with improved ‘egg crate’ trays and bomb shells. In the course of those tests, 30 fires were started — 22 of which went out on their own. New and more powerful incendiaries were ordered, and full-scale tests were planned for August 1944. However, when the Navy learned that it would take until mid-1945 to complete the tests, the 27-month, $2 million project was canceled — ‘not based on any shortcomings of the incendiary and time units developed,’ according to the notice, ‘but rather upon the shortcomings of the fundamental idea and the opportunity of getting sufficient reliable data in order to plan a timely operation.’

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