SM UC-57 was a German Type UC II minelaying submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. The U-boat was ordered on 12 January 1916, laid down on 14 March 1916, and was launched on 7 September 1916. She was commissioned into the German Imperial Navy on 22 January 1917 as SM UC-57. In seven patrols UC-57 was credited with sinking 5 ships, either by torpedo or by mines laid.
UC-57 disappeared in 1917 after landing a party of Finnish Jägers and 4 tons of munitions on the island of Hamnskär, circa 30km (20miles) from Loviisa, on 18 November. UC-57 was going to remain on the seabed overnight and then return to Germany but never arrived. She was probably sunk by a Russian mine.
A Type UC II submarine, UC-57 had a displacement of 415t when at the surface and 498t while submerged. She had a length overall of 50.52m (165.75feet), a beam of 5.22m (17.13feet), and a draught of 3.61m (11.84feet). The submarine was powered by two six-cylinder four-stroke diesel engines each producing 290PS300PS (a total of 580PS600PS), two electric motors producing 620PS, and two propeller shafts. She had a dive time of 48 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-57 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[1] | Fate[2] | |
|---|---|---|---|---|---|
| 9 June 1917 | Ludvig |  Sweden | 78 | Sunk | |
| 20 June 1917 | Penpol |  United Kingdom | 2,061 | Captured as prize | |
| 24 June 1917 | Meggie | United Kingdom | 1,802 | Captured as prize | |
| 26 June 1917 | Marie | 87 | Sunk | ||
| 26 June 1917 | Tervo | 58 | Sunk | ||
| 26 June 1917 | Georg | 18 | Sunk | ||
| 26 June 1917 | Martinniemi | 30 | Sunk |