Griffin summarized his memo by saying that, although ‘this proposal seems bizarre and visionary at first glance…extensive experience with experimental biology convinces the writer that if executed competently it would have every chance of success.’ He recommended an investigation ‘with all possible speed, accuracy and efficiency’ by the U.S. Army Air Forces. Bomb development was passed on to the Army Chemical Warfare Service.

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Adams and a team of naturalists were immediately authorized to find bats for experimentation. The team visited a number of likely sites in Texas and New Mexico where the bats could be found in large quantities — mostly in caves, but also under bridges, in barns and in large piles of rubbish. ‘We visited a thousand caves and three thousand mines,’ Adams said. ‘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 at driving. One car in our search team covered 350,000 miles.’

The team first investigated the mastiff bat, which they determined could carry a 1-pound stick of dynamite. But there was not a sufficient number of that variety available. The more common bat was the mule-eared or pallid species, which could carry 3 ounces. However, the naturalists concluded that the species was not sufficiently hardy for the work that needed to be done.

They finally settled on the Mexican free-tail bat for the project. Although it weighed only one-third of an ounce, experiments showed that it could fly fairly well with a payload of 15 to 18 grams. The Army’s Edgewood Arsenal in Maryland, near Washington, D.C., was to design an incendiary bomb weighing no more than 18 grams.

The largest colony of free-tails found during the search was an estimated 20 to 30 million that lived in the limestone Ney and Bracken caves near Bandera, in southwest Texas. At Ney Cave, U.S. Army Captain Wiley W. Carr reported that ‘five hours’ time 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.’

Capturing the bats was not difficult. Team members passed nets on long poles back and forth over the cave entrance as the bats emerged from their lairs. As many as 100 were captured in two or three passes, after which they were placed in a refrigerated truck. Adams took some to the Chemical Warfare Service headquarters at Aberdeen, Md., and released them to show Army officials how they could each carry a dummy bomb.

There was much opposition to the project from CWS officials, but in March 1943 the Army Air Forces issued authority for the project to proceed by a memo — Subject: ‘Test of Method to Scatter Incendiaries.’ Purpose: ‘Determine the feasibility of using bats to carry small incendiary bombs into enemy targets.’

Project members studied the habits of the bats intently. Louis F. Fieser, assigned as chief chemist for the Adams project, began to design bombs light enough to be carried by the free-tails. His research showed that the British had designed miniature bombs during World War I called ‘baby incendiaries’ made of thermite that weighed 6.4 ounces. Fieser made two sizes of incendiaries that were oblong celluloid cases filled with thickened kerosene. A small time-delay igniter fuse was attached along one side. One size weighed 17 grams and would burn for four minutes with a 10-inch flame. The other weighed 22 grams and would burn for six minutes with a 12-inch flame.

The time-delay igniter consisted of a firing pin held in tension against a spring by a thin steel wire. When the bombs were prepared for use, a copper chloride solution was injected into the cavity through which the steel wire passed. The copper chloride would corrode the wire in time; when it was completely corroded through, the firing pin snapped forward, striking the igniter head and lighting the kerosene.

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