Austria 1915, Przemysl balloon mail, blue balloon card with letter cancel \"K.u.k. Fortress artillery regiment prince Kinsky no. 3, fort balloon department\" (Kohl type IIIa) to Vienna, in the text dated 21.1.15, flight stamp \"balloon mail. \" and post office single circle postmark \"IX. 54\" in small type, red one-line cancel censored, rare superb document to the postal transport in unmanned balloon from the encircled city