The use of radio as a navigational aid was recognized early in its history. Its role now extends far beyond the initial basic function of direction finding, although that of course is important; in fact, it would be accurate to say that the electromagnetic spectrum is involved in all modern means of navigation; these include nondirectional radio beacons (NDB), long-range navigation (Loran-C), VHF omnidirectional radio range (VOR), and of course the Global Positioning System (GPS). Thus in this chapter and succeeding chapters we will learn of the different ways in which radio is involved. We begin with radio direction finding and the long-range radio navigation system called Loran-C which had been in use since 1958; prior to that, less accurate forms of long-range radio navigation had been in use since the second World War. On February 8, 2010, the US Coast Guard announced the termination of Loran-C services in the USA; it marked the end of a half a century of service that Loran-C had provided to mariners. The termination date for the Canadian portion of Loran-C was August 3, 2010. It was expected that other nations may retain local versions of radio beacons and Loran-C, since they are popular with fishermen and recreational mariners. The reason for the demise of Loran-C in North America is of course the revolutionary change in the technology of position finding brought on by the Global Positioning System, which will be described at length in succeeding chapters.