Luxembourg 1935 (July 17) This remarkable flight was organized by the famous rocketeer of the 1930s, Karl Roberti. The covers bear a 10c Intellectuals stamp with a "Visitez / Clervaux / Son Abbaye / Son Château" slogan cancellation as well as two private Roberti labels (one green, one brown) showing his rocket in flight above Clervaux. The two labels are cancelled with a purple cachet that reads "1. Raketenflug / Mit flüssige treibstoffen / (Kohlensäurerakete) / Clerf-Clervaux 17-7-35 / R.Kr.1 Luxemburgia" (translation: 1st rocket flight; With liquid propellant; (Carbonic acid rocket)). The cover is also signed by Roberti