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Capt. Lowell H. Smith and Lt. John P. Richter performing the first aerial refueling on June 27, 1923. The DH-4B biplane (right) remained aloft over the skies of Rockwell Field in San Diego, California, for 37 hours, using nine mid-air refuelings to transfer 687 US gallons (2,601 L) of aviation gasoline and 38 US gal (144 L) of engine oil.Photo credit: United States Air Force