I notice that OTRCAT.COM has posted an mp3 file of the circulating "Armistice Day Reunion" episode of the Empire Builders series. This is supposedly the earliest surviving recording of a network radio drama. It can be downloaded from this page:
Although the file is dated November 11, 1930, the program was actually broadcast the night before, on November 10, according to contemporary newspapers.
OTRCAT seems to think that Empire Builders was a local show but in fact it was a coast-to-coast NBC program from its New York beginnings in January 1929 to its final episode, broadcast from Chicago on June 22, 1931. Originally, Edward Hale Bierstadt wrote the scripts. Later, a wide variety of writers contributed, including our good friend Wyllis Cooper (back when he was still calling himself "Willis Cooper" or "W. O. Cooper").
I'm fairly certain that Cooper wrote this particular episode. His name isn't mentioned but the announcer says the author is "an American Army officer who was there" at the front when the Armistice was declared. That would be consistent with what's known about Cooper. Like the characters in the story, he served in the 131st Illinois Infantry. By 1930, he was in the Cavalry Reserve, having already been a captain in the Illinois National Guard.
Some of the ideas in the script crop up in his "Quiet Please" episode "Berlin, 1945" -- for example, the device of soldiers gathering on a holiday to reminisce (and having a fundamentally decent stranger among them mistaken for a spy!).