John Stack was an American aeronautical engineer who played an important role in the effort to achieve manned supersonic flight (see sound barrier). Stack graduated from the Massachusetts Institute of Technology in 1928 and then joined the Langley Aeronautical Laboratory, becoming director of all the high-speed wind tunnels and high-velocity airflow research there in 1939. Three years later he was named chief of the compressibility research division at Langley. In 1947, he was promoted to assistant chief of research, a title then changed to assistant director of the research center. Stack guided much of the research that paved the way for transonic aircraft, and in 1947 was awarded the Collier Trophy together Charles Yeager, the pilot who first broke the sound barrier. From 1961 to 1962 Stack was director of aeronautical research at NASA Headquarters before leaving to become vice president for engineering at Republic Aircraft Corp (later part of Fairchild Industries) from which he retired in 1971.