During World War II, the U.S. military needed to find accurate ways to guide missiles to their targets. Harvard University psychologist B. F. Skinner suggested that a missile nose cone be supplied with three compartments, each with a window. A pigeon would be placed in each section, and trained to peck on the window when the target appeared. If all three pigeons pecked, the weapon would be released. This prototype was never developed, but influenced later work on animal training.