Austria-Hungary's U-boat fleet was largely obsolete at the outbreak of
World War I, and over the first two years of the war the
Austro-Hungarian Navy focused its efforts on building a U-boat fleet for local defense within the
Adriatic. With boats to fill that need either under construction or purchased from Germany, efforts were focused on building ocean-going submarines for operation in the wider
Mediterranean, outside the Adriatic. To that end, the Austro-Hungarian Navy selected the
Stabilimento Tecnico Triestino (STT) A 6 design as the winner of a design competition for a new ocean-going submarine. The plans called for a boat that
displaced surfaced and submerged. The boats were to be long with a
beam of and a
draft of . For propulsion, the design featured two shafts, with twin
diesel engines of (total) for surface running at up to , and twin
electric motors of (total) for submerged travel at up to . The
U-52 class boats were designed for a crew of 40 men. The
U-52 design called for six torpedo tubes—four bow tubes and two stern tubes—and a complement of nine torpedoes. The original design specified two 10 cm/35 (3.9 in)
deck guns, which were superseded by two 12 cm/35 (4.7 in) deck guns in plans for the third and fourth boats. == Construction ==