 From the beginning of World War I, Austria-Hungary had been working to increase the size of its U-boat fleet, so the Imperial German Navy, which was finding it difficult to obtain trained submarine crews, sold two of its UB II boats, and , to its ally in June 1917.The German Type UB II design incorporated improvements over Type UB I boats, the first coastal submarines of the German Imperial Navy.Among these were twin engines and shafts for more redundancy during operations, a higher top speed, and larger torpedo tubes with double the complement of torpedoes.