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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."

Burrhus Frederic Skinner

Adams was very disappointed. He maintained that fires set by bat bombers could have been more destructive to Japanese cities than the two atomic bombs. He noted that bats had scattered up to 20 miles during the tests, adding, "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 small loss of life."

Meanwhile, tests had been ongoing for some time to train birds as kamikaze pilots. Burrhus Frederic Skinner, a behavioral psychologist at the University of Minnesota who believed that pigeons could be trained to guide missiles, originated the idea of using birds as bombers. A scientist noted for his view that learning occurred as a result of an organism responding to, or operating on, its environment, he did extensive research with animals, notably rats and pigeons, and concluded that a rat or pigeon could learn to press a lever in order to obtain food. Skinner wondered, after the Germans bombed Warsaw in 1939, whether a shell or missile could be designed that could be guided to a ground target from an aircraft. He was riding on a train at the time and saw a flock of birds lifting and wheeling in formation as they flew alongside the train. "Suddenly I saw them as ‘devices' with excellent vision and extraordinary maneuverability," he recalled. "Could they not guide a missile? Was the answer to the problem waiting for me in my own back yard?"

Skinner, who already had much experience with birds, chose to work with them in many experiments because they have better vision than humans, are faster in their movements, can distinguish colors, don't get airsick and are more easily handled than many other animals. He decided to focus on pigeons because he discovered that they are more predictable than other birds.

Skinner bought some pigeons at a poultry store and started teaching the birds to earn kernels of grain by pecking at a specific target image. During this training the birds were held in position in front of a screen by means of a special harness. "Feet and wings would be hard to harness," he reasoned, "but the head and neck might be used. The pigeon's eyes could pick out a target, movement of its neck could produce signals to steer the missile, and its head and neck together could pick up grain as a reinforcer.

"I found that I could conveniently package a pigeon in a man's sock with its head and neck protruding through a hole in the toe and its wings and legs drawn together at the back and lightly tied with a shoestring. The jacketed bird could be strapped to a block of wood and put into an apparatus."

Pigeon in a Skinner box

Skinner built a system in which the pigeon steered by moving pairs of lightweight rods around its neck. By lifting or lowering its head, the bird closed electrical contacts operating a hoist. By moving its head from side to side, it drove a hoist back and forth on an overhead track.

A bull's-eye was placed on a far wall of the room, a few grains of food were placed in a small cup in the center, and the apparatus was pushed toward it. By moving up or down and from side to side, the pigeon could reach the wall in position to take the grain.

"My pigeons became quite adept at this," Skinner recalled in his autobiography. "I pushed them faster and faster across the room until they were operating the moving hoist as fast as the motors permitted."

He next worked out a system whereby the pigeon pecks were picked up as an electronic signal and transferred to a control system. As the image moved off center, the pigeon would peck frantically to bring the device back on track; the resulting signals would operate the simulated missile control system to center the device on the target. With practice, his birds hit the target with near perfect accuracy and could easily distinguish one target from another.

Nose Cone, Pigeon-Guided Missile
1944

Skinner, convinced that his idea had merit, contacted members of the National Inventors Council, who were startled by the proposal and rejected the idea with the comment that it was unrelated to national defense. Undeterred, Skinner made his proposal to the NDRC on June 9, 1941, but again he received a polite "No."

News of the Pearl Harbor attack sparked Skinner to resume his work. He filmed his pigeons in action and again contacted the NDRC, and this time government scientists showed mild interest but felt it was a long shot. When A.D. Hyde, then head of the mechanical division of General Mills Inc., heard about the revolutionary idea, he was at first skeptical that pigeons could be trained as flying suicide bombs. However, he thought Skinner's reasoning was sound and persuaded the company's top management to back the project with technical help until it could be turned over to a government agency.

With this support, Skinner's system was refined. The previous harness was discarded in favor of a more practical lens and screen grid with a special servo-control mechanism. The force of the pigeon's pecking motion was increased by running a bomb's gyro and controls in a vacuum and by placing valves behind the top, bottom and sides of the flexible screen. When the pigeon tapped one of these valves, it opened, permitting air pressure to build up in the system and operate the fins on the bomb. When the target image was at dead center and the pigeon pecked at dead center, all the valves opened an equal amount and the setting was unchanged.

Detail of the three screens of the nose cone. A pigeon was behind each screen.

At this stage, the project showed enough promise that the newly formed Office of Scientific Research and Development (OSRD) awarded Skinner a contract in June 1943 under the name of Project Pigeon for "a homing device." The inventor "recruited" a squadron of 64 pigeons (40 homers and 24 ordinary pigeons) from local sources and began their training. The birds were left without food for 36 hours, then placed in a cage with some grain about 30 minutes a day.

The target for the actual bombing experiments, to be located in Florida, was a white pyramid on a green field, so Skinner used a screen of white triangles cut into green paper. Once a bird learned that pecking the white pyramids would produce a few kernels of grain, it was conditioned to expect to be fed when he saw them. As soon as the bird had learned to break through light paper, heavier sheets were substituted. Eventually the pigeon was pecking with the force of a miniature air hammer.

Once a bird had completed this "primary" training, it was graduated to an advanced trainer. This was a lightproof box mounted over a projection screen. A moving picture of a ground target appeared on this screen, and whenever the pigeon pecked it on the screen it caused an electrical contact to close and a small drawer to pop out containing kernels of grain.

Henschel Hs 293 (on trials) underneath an He-111 - 1942

This training worked well for a time, but the pigeons quickly learned they could get the grain no matter where they pecked the screen and began to disregard the target itself. Skinner outsmarted them by crossing two beams of light at right angles in front of the image. From then on, a pigeon had to peck the target image at dead center in order to break both beams of light and actuate a photoelectric relay to release the food.

Skinner then added a new tactic. He found he could feed the birds at regular time intervals or after a certain number of pecks. After a while, the pigeons learned to rap out as many as four pecks a second for more than two minutes without a break, and would work feverishly to prevent the target image from moving off dead center.

In one final test, Skinner put each bird into a hand-operated trainer. A person sat behind each pigeon and moved a color photo projected on the screen, at the same time operating the food magazine. The pigeon had to peck correctly or he got no food at all. According to the report on these experiments: "There wasn't a single washout in the entire class of 64. Every bird earned his wings with an A grade."

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Other experiments followed to test the birds' psychological fitness for battle. Target pistols were fired only a few inches from a bird's head. The pigeons didn't miss a peck, didn't even look up. Other extremely loud noises were introduced. Again, the pigeons stayed at their task. Skinner also put the pigeons in a pressure chamber, setting the altitude at 10,000 feet. They were also whirled around in a centrifuge, put on pure oxygen and exposed to bright flashes, simulating shell bursts. High vibrations were also introduced, and the birds were subjected to massive G forces without harmful effects.

HS-293

Following the success of those experiments, pigeons were placed in three, five and seven tandem positions in a missile to see whether, if one or more birds became obstinate or lazy, the majority could override any incorrect signals and keep the missile on course. The final test was to see whether a male pigeon placed alongside a female would abandon his task or vice versa. Once more, the birds' dedication to the mission was paramount. They pecked away at the target; hunger overcame any other desires. Skinner also learned that pigeons were seemingly fearless when feeding on hemp seed. They worked faster when it was used in place of the standard grain.

When sufficient data had been collected on the pigeons, it was sent to Washington for evaluation. Time passed, and Skinner was invited to OSRD to plead his case before a group of scientists. He brought a jacketed pigeon with him in a box, facing a translucent screen on which a target could be projected from across the room. He described what happened:

The pigeon had been in its jacket for 36 hours, and we had checked the box into and out of the baggage window at Chicago and had carried it with us on two long train rides. If the image on the screen was to be clear, the box would have to be closed, and I had installed a tube through which the pigeon could be watched without admitting too much light, but it would take too long to look down a tube, one person at a time, and I was asked to open the box. That meant that the pigeon saw a very faint image. Nevertheless, it performed beautifully, pecking steadily as we moved the target about. Someone put his hand in the beam from the projector and the pigeon stopped quickly. It started again just as quickly when the hand was withdrawn.

There could scarcely have been a better demonstration of the extraordinary predictability of behavior, the keenness of a pigeon's vision, the accuracy of its responses, and its freedom from distraction.

However, on October 8, 1944, Skinner and his associates were told that "further prosecution of this project would seriously delay others which in the minds of the Division have more immediate promise of combat application." Skinner, like Adams, was disappointed after so much effort had gone into his project. He commented in one of his books that if they meant other guided missile projects had more potential, "the United States had not only no way of guiding a missile but no missile worth guiding. The Germans were far ahead. In September 1943, long before our final meeting in Washington, they had used missiles controlled by radio from mother planes to wreak havoc on the American fleet landing soldiers at Salerno."

Skinner kept his pigeons at home and used the box he had taken to Washington to see if they would retain what they had learned. He tested them at six months, a year, two, four and six years later. All of them accurately struck the target, which enabled him to conclude his work had been worthwhile. While his pigeons were never tested in combat, he was confident they could have carried out their missions.

In the years following World War II, the U.S. Navy became more interested in missiles and their use against surface ships. The reports on Project Pigeon remained classified, but they were unearthed from the Navy files in 1948 and given new life under the designation Project Orcon (for organic control). The Naval Research Laboratory was tasked with "conducting a program of research to determine the feasibility of using pigeons as the sensing element for controlling missiles."

Tests were conducted over the next five years, using a sophisticated trainer that simulated a missile. The pigeon suspended inside faced a screen on which color photos of actual ships were projected. A metal contact was attached to its beak, and a flexible wire from it linked the bird to the missile.

SWOD MK 7 Pelican

A gridless screen made of electrically conducting glass tracked where the pigeon had pecked it. The servo-motors then steered the missile to a target ship, and the bird was rewarded with the usual kernels of corn. Repeated performances showed that the pigeons could guide missiles -- well enough under ideal conditions to score hits, although clouds, waves and shadows could throw them off course.

Project Orcon was canceled in 1953, when electronic guidance systems for missiles were deemed reliable. The Orcon test results, however, were kept under wraps for six more years before they were declassified. Meanwhile, there was an important spinoff from the research. The electrical conducting glass developed for the pigeon training became a key feature in the combat control centers of U.S. warships. It was employed by plotters using magnetic probes to trace the course of attacking aircraft.

Although bats and pigeons were never used to bomb enemy targets, the test results show that they could have. It is interesting to speculate what the results might have been if they had actually gone to war.