German cover sent on the Graf Zeppelin LZ127 airship's 1931 Polarfahrt / Polar Flight to Leningrad, USSR, and the Russian icebreaker Malygin. With Bordpost / on-board cancel. '01 CV EUR385 for flight. Totally philatelic -- but then again, 99% of Zeppelins are. Extremely unusual use with Danzig stamps. With photo cert