| U-120 | Type IIB |
| Feldpost Number | M 03 700 |
| Construction Yard | Flender Werke AG, Lübeck-Siems |
| Yard Number | 268 |
| Ordered | 28th Sep 1937 |
| Keel laid | 31st Mar 1938 |
| Launched | 16th Mar 1940 |
| Commissioned | 20th Apr 1940 |
| Baubelehrung | Marinelehrwerkstatt, Kiel / Baubelehrung U-Boote Ostsee, Kiel |
| Training, Flotillas and Duties |
| 04.40 - 06.40 | U Schule Flottille, Neustadt Schulboot (training boat)
|
| 07.40 - 03.45 | 21.U-Flottille, Pillau Schulboot (training boat)
|
| 03.45 - 05.45 | 31.U-Flottille, Wesermünde Ausbildungsboot (under training)
|
| Commanders |
| 04.40 - 11.40 | OL Ernst Bauer see also: U-126 |
| 11.40 - 05.41 | KL Wolfgang Heyda see also: U-434 |
| 05.41 - 02.42 | OL Willy-Roderich Körner see also: U-301 |
| 02.42 - 09.42 | OL Hans Fiedler see also: U-564 U-998 U-333 |
| 09.42 - 05.43 | LT Alfred Radermacher see also: U-5 U-393 |
| 07.43 - 09.44 | LT Joachim Sauerbier see also: U-56 U-251 |
| 09.44 - 05.45 | LT Rolf-Rüdiger Bensel |