Bidspirit auction | Worldwide Pioneer Flights - Danzig

Worldwide Pioneer Flights - Danzig - 1920 (October 26), Pioneer Flight registered cover from Danzig to Berlin (10.27) then to Copenhagen (10.29), franked by four stamps, including complete air post set, undelivered and returned to sender, F/VF, Est. $150-$200 , Sc. #C1-3