WLW operated under an experimental license with half a million watts from about 1935 to about 1940 when it was returned to 50KW.  It was still on a clear channel (700 Khz) with an efficient antenna so probably covered Europe especially to a high flying airplane.  The super power experiment was never duplicated.  However, the the transmitter was maintained for many years. Wikipedia has a good history of this period. I believe WLW still uses the same antenna .

My father was a Bombardier on B-24's in the Eighth Air Force during WW2.  Our family was from Lima, Ohio, long before I knew what a Command Set was he told me this story.  He said when they returned from a mission over Germany and were finally out of harm's way the radio operator would tune the radio to WLW in Cincinnati.  As I recall WLW in those days transmitted with far more than 50,000 watts.  He said it was like being home again.  Each time I restore a BC band command set I think of this.  Here is a link to a short Youtube I did one sunday morning with a broadband loop on a tripod outside my shop.  There was a station every 10KHz.  With that same configuration I can hear WWL in New Orleans, during the day, over 340 miles away.  Best Regards ... tom, N3LLL