In the United States, for most of the history of broadcasting, there were only three or four major commercial national terrestrial networks. From 1946 to 1956, these were ABC, CBS, NBC and DuMont (though the Paramount Television Network had some limited success during these years). From 1956 to 1986, the "Big Three" national commercial networks were ABC, CBS, and NBC (with a few limited attempts to challenge them, such as National Telefilm Associates [and its NTA Film Network] and the Overmyer Network). From 1954 to 1970, National Educational Television was the national clearinghouse for public TV programming; the Public Broadcasting Service (PBS) succeeded it in 1970.