In 1942, the local Chamber of Commerce persuaded the Parsons Corporation to move its Pureaire Unit Kitchen Division into the vacant sixty-year-old Greilick plant, and around the same time the Sheffer Collet Company also began operations in part of the same building. During World War II, Parsons turned to military production of helicopter blades there, reaching total employment of 700 including a rocket body plant on 12th Street. By the 1950's, Parsons had become the world's largest producer of helicopter rotor blades, eventually manufacturing or rebuilding 180,000 blades for 34 United States and foreign companies. Parsons and Sheffer Collet were forced to relocate to nearby Traverse City sites when Grandview Parkway was built in 1952. In 1946, Frank Stulen and James Gean pioneered procedures for performing aircraft engineering calculations on IBM punch card machines as part of efforts to expand rotor blade design capability. In 1948, while still at the Greilick plant, John T. Parsons and Frank Stulen developed the concept of numerically controlling machine tools, first using IBM punch cards and later magnetic tape. The process received a patent in 1958, and the concept revolutionized the control of machines and industrial processes throughout the world. The Society of Manufacturing Engineers recognized John T. Parsons as the father of numerical control in 1975, calling numerical control the beginning of the second industrial revolution and the start of an age in which control of machines and industrial processes passed from imprecise craft to exact science. In 1985, Parsons and Stulen received the National Medal of Technology from President Ronald Regan, and in 1993 Parsons was inducted into the National Inventors Hall of Fame. Traverse City became known as the birthplace of the Second Industrial Revolution.