Found this interesting article on how German subs were sent by RR to AH ports for assembly during WW 1.
The German Navy Mediterranean submarine flotilla
German submarines started with operations in the Adriatic Sea and in the Mediterranean Sea in the summer of 1915. In the first time the submarines (with German crews) operated under Austro-Hungarian flag and the each submarine temporarily had Austro-Hungarian submarines’ sign (i.e. serial numbers). Once when Germany declared war to Italy, on 28th August 1916, the submarines mainly returned under German flag. Their original serial numbers were returned as well. Because of some reasons, some of the submarines continued with operations under Austro-Hungarian flag and serial numbers.
The first German submarines (types "UB I" and "UC I") arrived in Pula from Germany by train, in pieces. Submarines UC 12, UC13, UC 14, UC 15 and UB14 were pieced together in the shipyard in Pula and started operations in June 1915.
Type "UB II" submarines (UB 42, UB 44, UB 45 and UB 46) also arrived in Pula by train. After the arrival, the submarines were pieced together in naval shipyard in Pula and started operating between March and June 1916.
"Mittel-U" class submarines arrived from Germany in the Adriatic by sea. Submarine U 21 (type U19) came in Kotor on 13th May 1915, for supplying and then proceeded to Turkey. Other "Mittel-U" class submarines arrived in the Adriatic later. Submarines U 34 and U 35 (type U31) arrived in August 1915. In September 1915 arrived submarines U 33 and U 39 (type U31). Submarine U 38 (type U31) arrived in November 1915. In the period between November and December 1916 arrived in the Adriatic submarines as follows: U 47 (type U43), U 32 (type U31) and U 63, U 64, U 65 (all three submarines were type U63).
"UC II" and "UB III" types of submarines were stronger and able to come from Germany to the Adriatic by sea. Table bellow shows times and numbers of the submarines’ arrivals in the Adriatic.