1/7/1939 The Golden Age of Detective Fiction is coined

January 7, 1939.  "The Golden Age of Detective Fiction" is the phrase most often used to describe the detective fiction of the 1920s and 1930s.  The term was apparently coined by John Strachey in an  article in The Saturday Review that appeared on this date. 

I found this out in Martin Edwards' excellent book The Golden Age of Murder.