The first delivery to a customer was to multi-millionaire Howard Hughes, who bought one 307 (NX-19904) for a round-the-world flight, hoping to break his own record of 91 hours 14 minutes set from July 10–14, 1938 in a Lockheed 14. Hughes' Boeing Stratoliner was fitted with extra fuel tanks and was ready to set out on the first leg of the round-the-world attempt when Nazi Germany invaded Poland on September 1, 1939, causing the attempt to be abandoned. This 307 later had the extra fuel tanks removed, was fitted with much more powerful Wright R-2600 engines, and was transformed into the luxurious "The Flying Penthouse" for Hughes, although it was little used, eventually being sold to oil tycoon Glenn McCarthy in 1949.