Poland / German Demokratic Republik (East Germany) 1958, cover with 80 Gr. pre-payment of postage in cash Koszalin 24. 3. 58" and Raketenvignette to 10 DM / 30Z, blue box stamp Bernau VERSUCHSFLUGPLATZ for ZIVILRAKETENFLUG and POSTRAKETENFUG" and black Polish Raketenflugstempel, cover above a little rough opening, rare!