The largest displacement aviation engine to be mass produced in the US.
But then there's this: Although mechanically reliable in flight, it developed an unenviable reputation for in-flight fires, particularly in its Boeing Stratocruiserapplication, and in addition the Wasp Major was maintenance-intensive. Improper starting technique could foul all 56 spark plugs; requiring hours to clean or replace.
Wasp Majors were produced between 1944 and 1955; 18,697 were built. Yep, I'd call that mass production.