1938
See Wikipedia for what was happening around the world in 1938.
Here are some Old Time Radio episodes that aired in 1938:
Mercury Theater
The Count of Monte Cristo
1938-08-29 (13.5 MB) [59:00]
Mercury Theater
War of the Worlds
1938-10-30 (11.74 MB) [51:17]
Plus 1 more episodes locked away in the Random Dispenser!