Air Mail cover 1916 (17 Feb.) Feldpost card to Vienna, flown Kumbor to Fiume by Navy seaplane, and showing a faint strike of the previously unrecorded "k.u.k. Seeflugstützpunkt/MIT KUSTENFLUGZEUG M4/BEFÖRDERT" cachet in red. Very rare. Ex Sobetzky and signed by Mikulski. Photo