SM UC-23 was a German Type UC II minelaying submarine or U-boat in the German Imperial Navy (de|Kaiserliche Marine) during World War I. The U-boat was ordered on 29 August 1915 and was launched on 29 February 1916. She was commissioned into the German Imperial Navy on 17 July 1916 as SM UC-23.[1] In 17 patrols UC-23 was credited with sinking 46 ships, either by torpedo or by mines laid. UC-23 was surrendered at Sevastopol on 25 November 1918 and broken up at Bizerta in August 1921.
Like all pre-UC-25 Type UC II submarines, UC-23 had a displacement of 417t when at the surface and 493t while submerged. She had a length overall of 49.35m (161.91feet), a beam of 5.22m (17.13feet), and a draught of 3.650NaN0. The submarine was powered by two six-cylinder four-stroke diesel engines each producing 250PS (a total of 500PS), two electric motors producing 460PS, and two propeller shafts. She had a dive time of 35 seconds and was capable of operating at a depth of .
The submarine had a maximum surface speed of and a submerged speed of . When submerged, she could operate for at ; when surfaced, she could travel at . UC-23 was fitted with six mine tubes, eighteen UC 200 mines, three torpedo tubes (one on the stern and two on the bow), seven torpedoes, and one 8.8sp=usNaNsp=us Uk L/30 deck gun. Her complement was twenty-six crew members.
| Date | Name | Nationality | Tonnage[2] | Fate[3] | |
|---|---|---|---|---|---|
| 29 November 1916 | Minnewaska |  United Kingdom | 14,317 | Sunk | |
| 31 December 1916 | Venus | 281 | Sunk | ||
| 21 February 1917 | HMS Princess Alberta | 1,586 | Sunk | ||
| 10 June 1917 | Kleopatra |  Greece | 160 | Sunk | |
| 13 June 1917 | Aghios Nicolaos | Greece | 120 | Sunk | |
| 14 June 1917 | New Zealand Transport | United Kingdom | 4,481 | Sunk | |
| 18 June 1917 | Pannomitis | Greece | 11 | Sunk | |
| 18 June 1917 | Xiphias | Greece | 483 | Sunk | |
| 19 June 1917 | Jakobus | Greece | 304 | Sunk | |
| 19 June 1917 | Maria | Greece | 35 | Sunk | |
| 19 June 1917 | Raxiarchos | Greece | 30 | Sunk | |
| 2 August 1917 | HMS Ermine | 1,777 | Sunk | ||
| 6 September 1917 | HMT Helgian | 220 | Sunk | ||
| 7 September 1917 | HMT By George | 225 | Sunk | ||
| 21 September 1917 | Santo Nicola | 159 | Sunk | ||
| 21 September 1917 | Spiridon | Greece | 128 | Sunk | |
| 23 September 1917 | Nicolaos | Greece | 104 | Sunk | |
| 19 January 1918 | Trocas | United Kingdom | 4,129 | Sunk | |
| 22 January 1918 | Evangelistria | Greece | 21 | Sunk | |
| 23 January 1918 | Birkhall | United Kingdom | 4,541 | Sunk | |
| 24 January 1918 | Aghia Arene | Greece | 16 | Sunk | |
| 24 January 1918 | Aghios Johannes | Greece | 14 | Sunk | |
| 20 February 1918 | Hagios Nicolaos | Greece | 18 | Sunk | |
| 20 February 1918 | Maria Archis | Greece | 13 | Sunk | |
| 20 February 1918 | Taxi Arches | Greece | 3 | Sunk | |
| 23 February 1918 | Aspasia | Greece | 105 | Sunk | |
| 28 February 1918 | Hagios Triast | Greece | 22 | Sunk | |
| 11 April 1918 | Trud | 610 | Captured as prize | ||
| 14 April 1918 | Unidentified lighter | 100 | Sunk | ||
| 14 April 1918 | Kazak | 622 | Captured as prize | ||
| 14 April 1918 | Olga | 327 | Captured as prize | ||
| 15 April 1918 | Rostov | 1,280 | Sunk | ||
| 3 October 1918 | Blasios | Greece | 181 | Sunk | |
| 3 October 1918 | Evangelistria | Greece | 35 | Damaged | |
| 5 October 1918 | Hagios Marcos | Greece | 45 | Sunk | |
| 5 October 1918 | Maria |  Spain | 2,159 | Sunk | |
| 5 October 1918 | Marigo | Greece | 48 | Sunk | |
| 5 October 1918 | Reventazon | United Kingdom | 4,050 | Sunk | |
| 13 October 1918 | Aghion Spiridon | Greece | 21 | Sunk | |
| 13 October 1918 | Aghios Georgios | Greece | 130 | Sunk | |
| 13 October 1918 | Biolleta | Greece | 99 | Sunk | |
| 13 October 1918 | Evangelistria | Greece | 41 | Sunk | |
| 13 October 1918 | Evangelistrios | Greece | 121 | Sunk | |
| 13 October 1918 | Glaros | Greece | 43 | Sunk | |
| 13 October 1918 | Iphigenia | Greece | 75 | Sunk | |
| 13 October 1918 | Panaghia | Greece | 26 | Sunk | |
| 13 October 1918 | Urania | Greece | 23 | Sunk | |
| 15 October 1918 | Evangelistria | Greece | 24 | Sunk | |
| 15 October 1918 | Georgios | Greece | 29 | Sunk | |
| 15 October 1918 | Maria | Greece | 43 | Sunk |