 The U @-@ 7 class was seen by the Austro @-@ Hungarian Navy as an improved version of its U @-@ 3 class , which was also a Germaniawerft design . As designed for the Austro @-@ Hungarian Navy , the boats were to displace 695 tonnes ( 684 long tons ) on the surface and 885 tonnes ( 871 long tons ) while submerged . The doubled @-@ hulled boats were to be 69 @.@ 50 metres ( 228 ft ) long overall with a beam of 6 @.@ 30 metres ( 20 @.@ 7 ft ) and a draft of 3 @.@ 79 metres ( 12 @.@ 4 ft ) . The Austrian specifications called for two shafts with twin diesel engines ( 2 @,@ 300 metric horsepower ( 2 @,@ 269 bhp ; 1 @,@ 692 kW ) total ) for surface running at up to 17 knots ( 31 km / h ; 20 mph ) , and twin electric motors ( 1 @,@ 240 PS ( 1 @,@ 220 shp ; 910 kW ) total ) for a maximum of 11 knots ( 20 km / h ; 13 mph ) when submerged . The boats were designed with five 45 cm ( 17 @.@ 7 in ) torpedo tubes ; four located in the bow , one in the stern . The boats ' armament was to also include a single 6 @.@ 6 cm ( 2 @.@ 6 in ) L / 26 deck gun . 
