"Chestnut's early control work concerned stability issues in electric power systems. The design and manufacturing of electric power system components - generators, transformers, motors, etc. was a major part of GE's activity then and now. During the Second World War Hal moved into aeronautics and ordinance divisions of the company and remained there until 1956. It was in the late 1940s that he wrote his first book. This pace-setting volume established his reputation as a leading figure in the international control community... Following retirement he concentrated on one of his long time passions in the control field - the potential for control concepts to provide insight into problems of international stability. It seems that his dedication to the use of control concepts in societal problems arose from his success in working with wary representatives from many countries to set up IFAC and with proud representatives from various US engineering societies to set up the AACC."