SM U-88 was a Type U 87 submarine built for the Imperial German Navy (Kaiserliche Marine) in World War I. U-88 was engaged in the naval warfare and took part in the First Battle of the Atlantic.
U-88 is most notable for sinking and taking with her Kapitänleutnant Walther Schwieger, responsible for sinking the when he was commander of . The submarine came to an end on 5 September 1917 when she struck a British mine and sank in the North Sea north of Terschelling at 53.95°N 59°W. Everyone on board U-88 was killed.
Type U 87 submarines were preceded by the shorter Type U 81 submarines. U-88 had a displacement of 757t when at the surface and 998t while submerged. She had a total length of 65.8m (215.9feet), a pressure hull length of 50.07m (164.27feet), a beam of 6.2m (20.3feet), a height of 9.35m (30.68feet), and a draught of 3.88m (12.73feet). The submarine was powered by two 2400PS engines for use while surfaced, and two 1200PS engines for use while submerged. She had two propeller shafts. She was capable of operating at depths of up to .
The submarine had a maximum surface speed of and a maximum submerged speed of . When submerged, she could operate for at ; when surfaced, she could travel at . U-88 was fitted with four torpedo tubes (two at the bow and two at the stern), ten to twelve torpedoes, one 10.5sp=usNaNsp=us SK L/45 deck gun, and probably one 8.8sp=usNaNsp=us SK L/30 deck gun. She had a complement of thirty-six (thirty-two crew members and four officers).
| Date | Name | Nationality | Tonnage[1] | Fate[2] | |
|---|---|---|---|---|---|
| 23 May 1917 | Hector |  Norway | 1,146 | Sunk | |
| 25 May 1917 | 6,329 | Sunk | |||
| 28 May 1917 | Roma | 417 | Damaged | ||
| 29 May 1917 | Ashleaf |  United Kingdom | 5,768 | Sunk | |
| 31 May 1917 | Jeanne Cordonnier |  France | 2,194 | Sunk | |
| 31 May 1917 | Miyazaki Maru |  Japan | 7,892 | Sunk | |
| 1 June 1917 | Cavina | United Kingdom | 6,539 | Sunk | |
| 6 June 1917 | Eemdijk |  Netherlands | 3,048 | Sunk | |
| 7 June 1917 | John Bakke | Norway | 1,611 | Sunk | |
| 29 June 1917 | Escondido | Norway | 1,066 | Sunk | |
| 3 July 1917 | Iceland | United Kingdom | 1,501 | Sunk | |
| 7 July 1917 | Coral Leaf | United Kingdom | 428 | Damaged | |
| 13 July 1917 | Ceres |  Denmark | 1,166 | Sunk | |
| 16 July 1917 | Vesta | Denmark | 1,122 | Sunk |