It was 1939, right in the Swing era and unfortunately also at the very start of World War II, a year that became immortal for music but also for such negative events. Glenn Miller is a prime example. A swing so cheerful and danceable (with the exception of Moonlight Serenade) proving that music (the happy kind) suffers no defeat even in hard and melancholic times like those of war.
"In The Mood" Glenn Miller & His Orchestra Bluebird B-10416 (August 1, 1939) SWING BIG BAND