 The title is a play on the card-playing term "ace in the hole" and the "flying ace" who would score five victories in a fighter aircraft.The "clipper" was a reference to the famous Boeing Clipper that had recently gone into service with Pan American World Airways.Even the fictional "PU-2" bore a striking resemblance to the Curtiss P-40 Warhawk fighter aircraft in service with the United States Army Air Corps.