1957
See Wikipedia for what was happening around the world in 1957.
Here are some Old Time Radio episodes that aired in 1957:
Secrets of Scotland Yard
Absent Minded Professor
1957-00-00 (12.24 MB) [26:44]
Secrets of Scotland Yard
Bank of England Robbery
1957-00-00 (12.95 MB) [28:16]
Secrets of Scotland Yard
Battalier
1957-00-00 (11.84 MB) [25:52]
Plus 34 more episodes locked away in the Random Dispenser!