U.S. Patent 1,665,594 "Telegraph printer" (Type 12 Teletype), filed June 1924, issued April 1928 U.S. Patent 1,745,633 "Telegraph receiver" (Type 14 Teletype), filed December 1924, issued February 1930 U.S. Patent 1,904,164 "Signalling system and apparatus therefor" (Type 15 Teletype) – filed July 1930, issued April 1933 U.S. Patent 3,507,997 "Frequency-Shift Teletypewriter" – filed August 1966, issued April 1970