some initial thoughts:

1. what (even approximate) date do you consider coverage to have started?
(i.e. the Munich Crisis,
invasion of Poland, 12-7-41?) This affects the two NBC networks Red and

2. "The Golden Web" by Erok Barnouw

3. NBC:LOC has their documents as well as the trove of broadcast recordings

4. CBS: I don't know where its corporate historical files are, but try The
Paley Center here in NYC. Google searches should include Ed Murrow, William
L. Shirer and Larry LeSueur