When pigeons were missile guidance systems

Guided missiles as offensive weapons made their debut during the Second World War. Most famous was the German V-2 missile, a liquid-fueled rocket that could deliver its one-ton payload to a target 200 miles away. Among the V-2's notable technological accomplishments was its control system of two gyroscopes for lateral stability. This was a more advanced guidance system than anything American scientists had at the time, though this wasn't for lack of trying: American scientists had been working on guiding missiles to targets throughout the war. Psychologist Burrhus Frederic (B. F.) Skinner got into the missile guidance game by researching a very non-traditional guidance system: pigeons.

The Animal Psychologist

B. F. Skinner happened upon psychology almost by chance. During a brief stint in New York City where he worked as a bookstore clerk, he read works by physiologists Ivan Pavlov and John Watson. Inspired, and curious to learn more, he enrolled as a student in Harvard’s Psychology Department at the age of 24. There, he found himself under the mentorship of the department chair William Crozier.

Crozier’s study of animals "as a whole" was in line with Skinner’s interest in correlating animal behavior with experimental conditions. Skinner worked with rats. He trained them to press a pedal, then changed the apparatus as the rats adapted to the experiment. Eventually, the graduate student developed a cumulative recorder of his rats' behavior that revealed the impact of continually changing the environment on their responses.

What Skinner discovered contradicted what he’d learned from Pavlov and Watson. The rate at which his rats pressed the pedal depended on what came after they pressed it, not whatever stimulus he offered them beforehand. This was a new development in the field, a phenomenon Skinner called "operant behavior." The overall process of using aftereffects to shape animal behavior he called "operant conditioning." Skinner spent five years studying this new field thanks to a fellowship, and synthesized his results in his first book, The Behavior of Organisms, which he published in 1938.

And then, the Second World War broke out. In short order, American scientists began developing missiles to use as offensive weapons. But the dearth of reliable missile guidance systems during the war opened the door for innovation, and B. F. Skinner stepped in with the novel suggestion to use pigeons to guide missiles to their targets. The pigeon-based guidance system was briefly applied to the Pelican missile program.

A pigeon near the three-bird demonstration nose cone. Via cyberneticzoo.com

Pigeon Guidance

In the spring of 1940, Skinner was at the University of Minnesota testing whether pigeons could steer themselves towards a specific target.

His setup was fairly simple. The pigeons were jacketed — swaddled in a sort of coat that so they could only move their heads and necks — and harnessed to a block. Freedom of pecking motion was key to the experiment as it was the pigeons’ head movements that controlled the motion of the system. The bird could ascend in the hoist by lifting its head up, descend by lowering its head, and move side to side by moving its head in the appropriate direction. This whole apparatus was mounted on wheels and aimed at a bulls-eye across a room. It was up to the pigeon to move its head and steer the apparatus. The incentive was grain at the center of the bulls-eye.

Skinner reasoned that a similar setup could be used to have pigeons guide missiles to their targets. If a pigeon could direct itself to a target from across the room in a hoist, it could guide a missile side to side using an even simpler setup. To test this idea, Skinner lowered a jacketed pigeon towards a revolving turntable onto which a target image was projected. The pigeon’s task was to steer itself towards the target by pecking left and right. Skinner found that pigeons could fairly easily be trained to hit images of ships during simulated descents by holding them up to screens and encouraging them to peck the target image.

The demonstration didn't garner much interest, in part because American missiles weren't yet developed to the point that they could reliably hit a target based on guidance at all. Undaunted, Skinner pressed on, and designed a second version of his proof-of-concept pigeon guidance system. This setup was housed in a truncated cone with a lens in the smaller end projecting the image of a target on a translucent plastic screen fixed at the wider end. The pigeon was trained to peck at the image of the target, and rewarded occasionally with grain. A guidance signal was determined from where on the screen the pigeon pecked.

Through these experiments, Skinner learned about the pigeons response rates, and figured out how and when to reinforce good behavior. He was ultimately able to hone his system, rewarding the pigeons at the correct intervals such that a bird was able to hold a missile steady on a point on a map for minutes at a time.

Pigeons for a Pelican

In February of 1943, on the strength of a favorable report from the Office of Scientific Research and Development, Skinner’s pigeon guidance system reached Washington. The system was sufficiently promising that the OSRD awarded a modest contract to General Mills to develop Skinner’s system.

Through this OSRD contract, the pigeon guidance system was assigned to the Pelican missile, the offshoot of the Bat missile still under development at the time. The missile used a guidance system like Skinner's test setup: a lens in the missile’s nose projected an image on a translucent plate within reach of a jacketed pigeon safely housed in a sealed pressure chamber. Every peck on the screen opened a corresponding air valve, sending orders a the servo system that relieved pressure outside the missile to guide its path to the real-life target.

It was also at this point in his work with pigeons that Skinner learned it is far easier to control a bird than a scientist: "It was very difficult to convince the latter that the former was an orderly system." To allay doubts about a pigeon’s reliability, Skinner developed a multi-bird system. Three birds in one missile created a majority rule situation. All three tracked the same target on separate screens. If one deviated from the other two, it was overruled, and the majority directions were transferred to the missile’s guidance system.

Though the multi-bird system worked, Skinner’s challenge remained convincing scientists that the system was viable. Unbeknownst to the psychologist, the advent of radar was making his pigeon guidance system obsolete before it ever flew.

Skinner with pigeons. via archaid.org

Pigeons after Project Pigeon

The Pelican missile program was finally cancelled in September of 1944, supplanted by the original Bat missile as per the original National Bureau of Standards specifications. The Bat was a winged glider capable of traveling 15 to 20 miles from its aerial drop point to enemy ships and off-shore targets. For steering, the Bat used a controllable tail elevator driven by an autopilot system and servo motors.

Like the V-2, the Bat debuted late in the war. It first saw combat in 1945 off the coast of Borneo, destroying several Japanese ships during its short operational lifetime. The Bat was retired with the war’s end.

But Pelican’s cancellation wasn't the end of pigeon-based guidance systems. Once American scientists discovered the advanced German guidance systems after the war, homing systems not only became important, they became vital. A psychologist with the Naval Research Laboratory named Franklin V. Taylor took a particular interest in living organism’s ability to respond to visual patterns and steer a missile to its target. The pigeon-guidance was resurrected by the NRL for investigation as Project ORCON (for "organic control"). Under ORCON, pigeons' beaks were tipped in gold, and the translucent pecking surface turned into a semi-conducting one to create a much more sensitive and precise control system.

In the end, pigeons were never used as a guidance system in combat missiles, but that doesn’t mean the project was a waste. Aside from demonstrating the power of animal conditioning, the program highlighted how war changes the way we relate to living organisms: using them as part of a weapons system. It also, as Skinner said, showed that in certain circumstances crackpot ideas are worth exploring, even if it's only as a proof of concept.

Sources: “Pigeons in a Pelican” by B. F. Skinner; Project Pigeon; Skinner: B. F. Skinner Homepage; B. F. Skinner Biography; Air Air Force Science Advisory Group Report “Guided Missiles and Pilotless Aircraft” by Hugh Dryden et at, 1944.

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