What was a four-course radio used for in aviation?

A four-course radio was utilized in aviation primarily as a navigation aid that marked four distinct courses to and from specific radio stations. This technology played a significant role in helping pilots maintain their intended flight paths during navigation, especially before the advent of more advanced systems like GPS. By following these courses, pilots could ensure they stayed on track while flying to or from a given location, greatly enhancing the safety and reliability of air travel during a time when navigational aids were limited in scope.

The focus on low to medium frequencies in the description highlights the operational range of this system, which was well-suited for the communication and navigation needs of the era. Aviation navigation relied on radio signals to provide guidance, and a four-course radio system allowed pilots to determine their position relative to the navigational aids, making it a crucial tool in early aviation.