Ostropa block (unfortunately somewhat affected by the sulphurous rubber) on registered letter Frankfurt April 29, 1936 with decorative additional franking transported to Lakehurst with the first North American flight of the airship Hindenburg. Very rare use of the block on zeppelin mail. The letter was subject to foreign exchange control and was opened by customs and sealed again with a seal. Slight traces of transport. Great record, 1 year before the Lakehurst airship burst into flames.