sentences:  Civilian development of aerial refueling in Great Britain was more successful, but in the end it, too, was disregarded.However, Spaatz, two decades after the flight of the "Question Mark", became head of the United States Air Force and using the British system as a starting point, implemented in-flight refueling on a worldwide operational basis.The first complete inflight refueling between two aircraft took place on June 27, 1923, when two Boeing-built de Havilland DH-4Bs of the United States Army Air Service accomplished the feat over San Diego's Rockwell Field.