Type U 20

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Type U 20 (“Havmanden”-Boote)
U 20 to U 23 = 4 U-boats

In view of the modest number of Austro-Hungarian U-Boats at the outbreak of World War I early soundings concluded for a particular favourable solution through the type “Havmanden” submarines of the Danish Navy, of which a first of a total of 6 submarines was commissioned already on 20 August 1912, the remaining submarines until July 1914.

Construction of 4 of these single hull U-Boats was authorized in March 1915, to be managed by a specially founded company “Ungarische Unterseebootsbau AG”/ UBAG (= “Hungarian Submarine Construction inc.”) and to be built equally at the Pola Arsenal (U 20 and U 23) as well as the Whitehead Shipyard at Fiume (U 21 and U22). However, the construction, originally scheduled to last 15 months, went much slower than planned, partially caused by the frequent quarrel between Austrian and Hungarian companies about shipbuilding for the Austro-Hungarian Navy.

As an example, keel laying of U 20 occurred on 29 September 1915, whereas commissioning could not be executed before 20 October 1917. Also, the three remaining U-boats were not commissioned before August and November 1917.


Year of Construction



U 20 and U 23 at Seearsenal Pola,

U 21 and U 22 at Whitehead-shipyard/ UBAG at Fiume


165 t / 204 t submerged


38.8 m


3.6 m


2.8 m


1 diesel engine, 1 electric engine, 1 propeller

Engine power

450 HP/ 160 HP submerged


13.2 kn/ 9 kn submerged


750 nm at 12 kn/ 71 nm at 2.3 kn submerged

Diving depth

50 m



2 bow torpedo tubes, 2 torpedoes, 1 MG, later 1 x 7.0 cm gun