[4][5] In the early 1930s, the Adcock antenna (transmitting in the LF/MF bands) became a key feature of the newly created radio navigation system for aviation.
The low frequency radio range (LFR) network, which consisted of hundreds of Adcock antenna arrays, defined the airways used by aircraft for instrument flying.
The same principles remain valid today, and the Adcock antenna array and its variants are still used for radio direction finding.
The result was a network of electronic airways, which allowed pilots to navigate at night and in poor visibility, under virtually all weather conditions.
The LFR remained as the main aerial navigation system in the U.S. and other countries until the 1950s, when it was replaced by VHF-based VOR technology.