D.C., although a blurry demonstration broadcast showed that it would not be in regular use for several months. The DuMont Television Network, which had begun experimental broadcasts before the war, launched what Newsweek called "the country's first permanent commercial television network" on 15 August 1946, connecting New York City with Washington. Not to be outdone, NBC launched what it called "the world's first regularly operating television network" on 27 June 1947, serving New York City, Philadelphia, Schenectady and Washington. Baltimore and Boston were added to the NBC television network in late 1947. DuMont and NBC would be joined by CBS and ABC in 1948. In the 1940s, the term "chain broadcasting" was used when discussing network broadcasts, as the television stations were linked together in long chains along the East Coast. But as the television networks expanded westward, the interconnected television stations formed major networks of connected affiliate stations. In January 1949, with the sign-on of DuMont's WDTV in Pittsburgh, the Midwest and East Coast networks were finally connected by coaxial cable (with WDTV airing the best shows from all four networks). By 1951, the four networks stretched from coast to coast, carried on the new microwave radio relay network of AT&T Long Lines. Only a few local television stations remained independent of the networks. Each of the four major television networks originally only broadcast a few hours of programs a week to their affiliate stations, mostly between 8:00 and 11:00 p.m. Eastern Time, when most viewers were watching television. Most of the programs broadcast by the television stations were still locally produced. As the networks increased the number of programs that they aired, however, officials at the Federal Communications Commission (FCC) grew concerned that local television might disappear altogether. Eventually, the federal regulator enacted the Prime Time Access Rule, which restricted the amount of time that the networks could air programs; officials hoped that the rules would foster the development of quality local programs, but in practice, most local stations did not want to bear the burden of producing many of their own programs, and instead chose to purchase programs from independent producers. Sales of television programs to individual local stations are done through a method called "broadcast syndication", and today nearly every television station in the United States obtains syndicated programs in addition to network-produced fare. Late in the 20th century, cross-country microwave radio relays were replaced by