the Foundation fund development of a working model. This allowed Newhouse to build an experimental machine which formed the basis of his 1930 Master's thesis, in partnership with J. D. Corley. The device was taken to Wright Field where it was tested by Albert Francis Helgenberger, a noted expert in aircraft navigation. Hegenberger found that the system worked as advertised, but stated that it would have to work at higher frequencies to be practical. Espenschied and Newhouse Espenschied had also been considering the use of Appleton's idea for altitude measurement. In 1926 he suggested the idea both as a way to measure altitude as well as a forward-looking system for terrain avoidance and collision detection. However, at that time the frequency of available radio systems even in what was known as shortwave was calculated to be fifty times lower than what would be needed for a practical system. Espenschied eventually filed a patent on the idea in 1930. By this time, Newhouse had left Ohio State and taken a position at Bell Labs. Here he met Peter Sandretto, who was also interested in radio navigation topics. Sandretto left Bell in 1932 to become the Superintendent of Communications at United Air Lines (UAL), where he led the development of commercial radio systems. Espenschied's patent was not granted until 1936, and its publication generated intense interest. Around the same time, Bell Labs had been working on new tube designs that were capable of delivering between 5 and 10 Watts at up to 500 MHz, perfect for the role. This led Sandretto to contact Bell about the idea, and in 1937 a partnership between Bell Labs and UAL was formed to build a practical version. Led by Newhouse, a team had a working model in testing in early 1938, and Western Electric (Bell's manufacturing division) was already gearing up for a production model. Newhouse also filed several patents on improvements in technique based on this work. Commercial introduction The system was publicly announced on 8 and 9 October 1938. During World War II, mass production was taken up by RCA, who produced them under the names ABY-1 and RC-24. In the post-war era, many companies took up production and it became a standard instrument on many aircraft as blind landing became commonplace. A paper describing the system was published jointly by Espenschied and Newhouse the next year. The paper explores sources of error