Felsenthal CPU-73 A/P Air Navigation Attack Computer

The Felsenthal CPU-73 A/P Air Navigation Attack Computer is a special purpose circular slide rule made for the United States Air Force and manufactured by the Felsenthal Instrument Corporation. Designed to calculate the course required for a fighter pilot to intercept a moving target, it is 9 inches in diameter.
During World War II, Felsenthal produced over 75% of the plastic calculating instruments used by the Army Air Forces, and over 90% of those used by the Navy Bureau of Aeronautics. After the war, it introduced a variety of plastic items for commercial and technical purposes. Located in Chicago, it was known as G. Felsenthal & Sons in the 1940s, G. Felsenthal & Sons, Inc. in the 1950s, Felsenthal Plastics Inc. in 1971, and Felsenthal Instrument Co. in 1972.