Based on an original so-called block sketch dated May 1917 handed over by the commissary of police at Vlissingen to the Dutch naval staff
Building ordered on 15 October 1914, laid down by Germaniawerft, Kiel, Germany with yard number 245 on 30 November 1914, launched in April 1915, commissioned on 6 May 1915, to be handed over to Bulgaria bur lost after 27 September 1916 underway from Varna, Bulgaria towards Sevastopol, Russia before delivery could be executed. Submarines of this type served in the German (UB-1 class), Austro-Hungarian (U-10 class) and Bulgarian navies. Preceded by the UA and succeeded by the UB II class (SM-18-SM-47).
General technical class characteristics. Displacement 127 (surfaced)-142 (submerged) tons and as dimensions 23,62 (pressure hull)-27,88/28,10 (over all) x 3,15 x 7,30 (depth) x 3,03 (draught) metres or 77.6-91.6/92.2 x 10.4 x 23.11 x 9.11 feet.. The machinery consisted of 1 diesel engine and 1 electric motor driving one screw allowing a speed of 6,47 (surfaced)-5.5 (submerged) knots and a surfaced range of 1.860 nautical miles with a speed of 5 knots and submerged 45 nautical miles with 4,5 knots. Test depth 50 metres/160 feet and able to dive within 33 seconds. Their crew numbered 14 men. The armament consisted of 2-45cm/17.7” torpedo tubes in the bow for which 2 torpedoes were carried and 1-0,8cm/0.31” machinegun.