competitive evaluation. Based on the trials results, the Austro-Hungarian Navy determined the characteristics that the next generation of Austro-Hungarian submarines should have. They were looking for a double-hulled submarine of about displacement with diesel propulsion. They also wanted a surface speed of , and for the boat to be armed with between three and five torpedo tubes. The Austro-Hungarian Navy selected the Germaniawerft 506d design, also known as the Type UD, for the U-7 class over the Type 48 design submitted by Whitehead & Co., primarily because of the lower cost. The Navy ordered five boats on 1 February 1913. Design The U-7 class was seen by the Austro-Hungarian Navy as an improved version of its , which was also a Germaniawerft design. As designed for the Austro-Hungarian Navy, the boats were to displace on the surface and while submerged. The doubled-hulled boats were to be long overall with a beam of and a draft of . The Austrian specifications called for two shafts with twin diesel engines ( total) for surface running at up to , and twin electric motors ( total) for a maximum of when submerged. The boats were designed with five torpedo tubes; four located in the bow, one in the stern. The boats' armament was to also include a single /26 deck gun. Construction After the Austro-Hungarian Navy's 1 February 1913 order, the first two boats, U-7 and U-8, were laid down at Germaniawerft on 1 November. U-9 was laid down at the end of December, and the final two boats, U-10 and U-11 were both begun in February 1914. Construction of the boats was slated to be complete within 29 to 33 months. None of the submarines were complete when World War I began in August 1914. With the boats under construction at Kiel, the Austrians became convinced that it would be impossible to take delivery of the boats, which would need to be towed into the Mediterranean past Gibraltar, a British territory. As a result, the five boats of the class were transferred to the Imperial German Navy on 28 November 1914 after the advance payment of 2 million Kronen had been returned. Germaniawerft was then awarded Kriegsauftrag D, hence the type was known as UD. After their purchase, the boats were assigned the numbers U-66 to U-70, and the class became known as the U 66 type. The Imperial German Navy had