Building ordered on 25 November 1910, laid down at the Kaiserliche Werft Danzig with yard number 14 on 7 November 1911, launched on 18 December 1912, commissioned on 5 August 1913, sunk the British passenger ship RMS Lusitania on 7 May 1915, grounded on the Danish coast on 4 November 1915 and scuttled by her own crew 5 November 1915. Destroyed during the First World War 36 ships with a total gross tonnage of 144.300 tons.
Double hulled project type 20 submarine wit as sister ships U 20, U 21 and U-22 which were the first German submarines fitted out with diesel engines. Displacement 650 (surfaced)-873 (submerged) tons and as dimensions 64,15 x 6,10 x 3,58 metres or 210.6 x 20.0 x 11.9 feet. Maximum test diving depth 50 metres/164.1‘. Machinery consisted of 2-6 cylinder 850 hp MAN diesel engines and 2-600 hp AEG double Motordynamos allowing a speed of 15,4 (surfaced)-9,3 (submerged) knots. Range surfaced with a speed of 8 knots 9.700 nautical miles and submerged with a speed of 5 knots 80 nautical miles. Crew numbered 35 men included 4 officers. Original armament 4-50cm torpedo tubes (bow 2, stern 2) or which she carried 9 torpedoes and 1-8,8cm gun until 1916. Since then 2-8,8cm L/30 quick firing guns and 1-3,7cm/1.5” Hotchkiss gun.
