In the First World War, Imperial German submarines had been transported via rail to the Pola Flotilla based in the Adriatic. With Turkey as an ally of the Central Powers, the Imperial German Navy could also access the Black Sea via the Dardanelles and the Bosphorus, where the Constantinople Flotilla was based. In the Second World War, during Operation Barbarossa, the "Luftwaffe" engaged the Soviet Black Sea Fleet, but at the Romanian Siege of Odessa (1941), the evacuation of the Red Army forces via the sea could not be prevented with the meagre naval forces available. In October 1942, the 30th Flotilla under the command of Kptlt. Helmut Rosenbaum was founded. With Turkey remaining neutral, access via the Bosphorus was not feasible. It was decided that small vessels, torpedo boats and U-boats, should be transported from the German Bight via the Danube to the Black Sea. The predecessor to the modern Rhine–Main–Danube Canal, the 19th century Ludwigskanal, was not suitable, though, so transport via land was necessary.