What were NBC Red and NBC Blue,   what did they become  and why?

NBC, the National Broadcasting Company, established the first US radio network of 14 stations in 1926, although previously there had been loose associations of independent stations.
NBC was a collaborative venture between RCA, Westinghouse and GE.
The AT&T station WEAF New York originated most of the programming,  and its name was changed to WNBC.

This was the original NBC Red network, so-called because of the coloured pencil lines on AT&Ts long-distance telephone distribution maps.

The Blue Network was a group of stations acquired in 1927 centred on WJZ New York.
In the 30s NBC expanded across the whole USA.
Rival network the Columbia Broadcasting System began in 1927.

In 1943 NBC was forced by anti-trust law to sell the Blue network, which later became ABC - the American Broadcasting Company.

NBC sold all its interests in radio in 1986.
The radio network which currently calls itself NBC is nothing whatever to do with NBC television.

see   sidebar - US and British Broadcasting history