This classification exists to ensure the viability of cross-country or cross-continent radio service enforced through a series of treaties and statutory laws.
Cuba was originally included in the plan and had several stations given clear-channel status, but stopped participating after the Cuban Revolution of 1959.
Sixty medium wave frequencies were set aside in 1941 under the North American Regional Broadcasting Agreement (NARBA) for use by usually only one, although in some cases two or three, AM stations, covering a wide nighttime area via skywave propagation.
Such stations are allowed three manners of operation after sunset; to sign off the air completely until sunrise, reduce power (sometimes dramatically, to only a few watts), or switch to a nighttime-only frequency (such as the Detroit area's WNZK, which broadcasts on 690 during the day, and on 680 at night).
Many of the Class B frequencies were assigned to a single station, although a few were used on both the East and West coasts, which were considered far enough apart to limit interference.
Problems intensified in the summer of 1926, when a successful challenge was made to the government's authority, under the Radio Act of 1912, to assign station transmitting frequencies and powers.
[12] The Federal Radio Commission (FRC) was formed in March 1927, and one of its key tasks was to reorganize the chaotic broadcast band.
[13] A December 1, 1927 report on the FRC's ongoing work reviewed operations on 600 to 1000 kHz, which divided these frequencies into ones that were considered "clear" and "unclear".
On November 11, 1928, the FRC implemented General Order 40, which classified AM band frequencies as Local, Regional or Clear.
The licensees of clear-channel stations argued that, without their special status, many rural areas would receive no radio service at all.
On June 13, 1938, the U.S. Senate adopted resolution 294, sponsored by Burton K. Wheeler (D-Montana), which stated that it was the "sense of the Senate... that the Federal Communications Commission should not adopt or promulgate rules to permit or otherwise allow any station operating on a frequency in the standard broadcast band (550 to 1600 kilocycles) to operate on a regular or other basis with power in excess of 50 kilowatts".
Other broadcasters, particularly in the western states, argued to the contrary; that if the special status of the clear-channel stations was eliminated, they would be able to build facilities to provide local service to those rural "dark areas".
Because FM and TV stations did not yet exist, the FCC's main intent for the clear-channel assignments was to provide reliable radio service to the thousands of Americans who lived in the vast rural areas of the United States.
One of the most outspoken of the small-town broadcasters, Ed Craney of KGIR in Butte, Montana, went so far as to apply to move his station, then on the 1370 kHz regional channel, to a class I-A signal on 660 kHz, asking the FCC to downgrade the NBC New York flagship, WEAF, to make way for the Butte station.
After 1941, several clear-channel stations applied for power increases to between 500 and 750 kW;[18][19] with dissemination of national defense information cited as one reason this would be in the public interest.
KOB eventually won the argument in the late 1960s; it and several other western stations were allowed to move to eastern clear channels.
These new Class II-A assignments (in places like Boise, Idaho; Las Vegas and Reno, Nevada; Lexington, Nebraska; Casper, Wyoming; Kalispell, Montana; and others) began what would later be called "the breakdown of the clear channels".