In 1934, the Department of Commerce renamed the Aeronautics Branch the Bureau of Air Commerce to reflect the growing importance of aviation to the nation. In one of its first acts, the Bureau encouraged a group of airlines to establish the first air traffic control centers (Newark, New Jersey; Cleveland, Ohio; and Chicago, Illinois) to provide en route air traffic control. In 1936, the Bureau took over these centers. Early en route controllers tracked the position of planes using maps and blackboards and little boat-shaped weights that came to be called "shrimp boats." They had no direct radio link with aircraft, but used telephones to stay in touch with airline dispatchers, airway radio operators, and airport traffic controllers. Although en route ATC became a federal responsibility, local government authorities continued to operate airport towers. While the Department of Commerce worked to improve aviation safety, a number of high profile accidents called the department's oversight responsibilities into question. A 1931 crash that killed all on board, including popular University of Notre Dame football coach Knute Rockne, elicited public calls for greater federal oversight of aviation safety. Four years later, a DC-2 crash killed U.S. Senator Bronson Cutting of New Mexico.