They also wanted a surface speed of 16–18 knots (30–33 km/h; 18–21 mph), and for the boat to be armed with between three and five 45 cm (17.7 in) torpedo tubes.[1] 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.[4] The Navy ordered five boats on 1 February 1913.[3]