- 1 * MTU 16V 396 marine diesel engine
- 9 * HDW/Siemens PEM fuel cells, 30–40 kW each
- 1 * Siemens Permasyn electric motor 1700 kW
- 1 * shaft
- 1 * seven-bladed skewback propeller
- CSU 90 (DBQS-40FTC) compact sonar
- Kelvin Hughes Type 1007 I-band navigation radar
- ISUS 90 integrated sensor and weapon control system
- EADS FL 1800U electronic warfare self-protection system
- 6 * 533 millimetres (21 in) torpedo tubes (in 2 forward pointing groups of 3)
- 13 * DM2A4 Black Shark torpedo
- or IDAS missiles
- 24 * external naval mines (optional)
U-31 (S181) is a Type 212A submarine of the German Navy, and the lead ship of her class.
U-31 was built by TKMS, with construction taking place at the shipyards of Thyssen Nordseewerke of Emden and Howaldtswerke at Kiel. Launched on 20 March 2002, U-31 was commissioned alongside her sister ship U-32 by German Minister of Defence Peter Struck in Eckernförde on 19 October 2005. U-31 is propelled by one diesel engine and an electric motor driven by nine fuel cells, making the submarine virtually undetectable.