The Vistula Flotilla was created on 30 July 1914, two days after Austria declared war on Serbia. At that time, a handful of steamers were commandeered, equipped with armor plating and cannons and deployed to protect Austrian shipping from Russian attacks. Headquartered at Krakow and initially operating out of bases at Niepolomice and Nadbezezie in Austrian Galicia, the flotilla extended its activity northward after the successful campaign of 1915 when the Russians were driven out of Poland. Later, the gunboats served largely as escorts (primarily against attacks by bandits) for the tugs and barges moving supplies for the military forces operating further to the east
Sailors and other personnel of the flotilla could send cards and letters free of postage as members of the Austro-Hungarian military forces. In facts the only stamps seen on flotilla mail come on clippings from parcel cards used to send packages home. In order to qualify for free franking, an official unit cachet to be applied to the covers. To satisfy this need, a substantial variety of such markings were produced, thus providing the primary basis for the story in this story.
Note cachets of the "Imperial & Royal Military Headquarters in Krakow" (in black) and the "I & R Vistula Flotilla" (in violet).
With patience and diligent search, Vistula Flotilla mail can be acquired. However, it is collected by a number of avid philatelists, especially specialists in Polish material. As a result, competition for unusual items is keen. In fact, some of the unit markings are very elusive, and assembling the examples shown here has taken more than two decades.
By 1916, the headquarters of the flotilla had moved to Niepolomice, about a dozen miles downstream from Krakow. Von Philippovic was still the commander but had been promoted to Captain, as confirmed by this postcard he mailed to his wife in Zagreb. It has three cachets: one for the "Headquarters of the I & R Vistula Flotilla." while the others are generic markings and indicate "Military Service/Postage Free" and "to be Forwarded."This fieldpost cover was sent by First Lt. of Engineers Polivka, who was the commander of S.M.S. Polonez, to flotilla commander Capt. von Philippovic in Niepolomice and is marked with the official cachet of the ship. Mail other than cards and letters required payment of postage, thus these examples from packages sent by the sailors provide examples of prepaid franking. As shown by the cachets, these items originated from S.M.S. Melszryn and S.M.S. Neptun but presumably posted at the nearest civil post office.