|Ordered:||5 June 1941|
|Builder:||DeSchiMAG AG Weser, Bremen|
|Laid down:||21 October 1942|
|Launched:||17 April 1943|
|Commissioned:||2 August 1943|
|Fate:||probably sunk by mine in position Coordinates: on 17/18 September 1944|
|Class and type:||Type IXC/40 submarine|
|Height:||9.60 m (31 ft 6 in)|
|Draught:||4.67 m (15 ft 4 in)|
|Test depth:||230 m (750 ft)|
|Complement:||4 officers, 44 enlisted|
|Identification codes:||M 53 689|
German Type IXC/40 submarines were slightly larger than the original Type IXCs. U-855 had a displacement of 1,144 tonnes (1,126 long tons) when at the surface and 1,257 tonnes (1,237 long tons) while submerged. The U-boat had a total length of 76.76 m (251 ft 10 in), a pressure hull length of 58.75 m (192 ft 9 in), a beam of 6.86 m (22 ft 6 in), a height of 9.60 m (31 ft 6 in), and a draught of 4.67 m (15 ft 4 in). The submarine was powered by two MAN M 9 V 40/46 supercharged four-stroke, nine-cylinder diesel engines producing a total of 4,400 metric horsepower (3,240 kW; 4,340 shp) for use while surfaced, two Siemens-Schuckert 2 GU 345/34 double-acting electric motors producing a total of 1,000 shaft horsepower (1,010 PS; 750 kW) for use while submerged. She had two shafts and two 1.92 m (6 ft) propellers. The boat was capable of operating at depths of up to 230 metres (750 ft).
The submarine had a maximum surface speed of 18.3 knots (33.9 km/h; 21.1 mph) and a maximum submerged speed of 7.3 knots (13.5 km/h; 8.4 mph). When submerged, the boat could operate for 63 nautical miles (117 km; 72 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 13,850 nautical miles (25,650 km; 15,940 mi) at 10 knots (19 km/h; 12 mph). U-855 was fitted with six 53.3 cm (21 in) torpedo tubes (four fitted at the bow and two at the stern), 22 torpedoes, one 10.5 cm (4.13 in) SK C/32 naval gun, 180 rounds, and a 3.7 cm (1.5 in) SK C/30 as well as a 2 cm (0.79 in) C/30 anti-aircraft gun. The boat had a complement of forty-eight.
U-855 was ordered in June 1941 from DeSchiMAG AG Weser in Bremen under the yard number 710. Her keel was laid down on 21 October 1942 and the U-boat was launched the following year on 17 April 1943. She was commissioned into service under the command of Kapitänleutnant Albert Sürenhagen (Crew 36) in 4th U-boat Flotilla.
In April 1944 Sürenhagen handed over command to Oberleutnant zur See Prosper Ohlsen (Crew 36). U-855 transferred to the 10th U-boat Flotilla for front-line service and left Kiel for operations in the North Atlantic on 22 June 1944, but experienced engine problems which forced her to return to Kiel. The U-boat left Kiel again on 1 July and served as a weather boat in the North Atlantic until September 1944.
An attack on an unescorted freighter on 6 September 1944 was not successful. The next day U-855 met with 516 and supplied her with provisions for twelve days. The following day, 9 September, she refuelled U-516 before making for port. Her last transmission was received on 11 September 1944, after that the U-boat was missing.
Since U-855 would have had to pass through known mine barrages about a week into her return voyage. Since she failed to report the successful passage, as other U-boats would do, she was probably sunk by a mine in the Northern Barrage on 17 October. That day another U-boat in the vicinity, U-804 reported hearing an explosion of a mine. The previous assumption that U-855 was attacked and sunk by a British aircraft, Liberator 'A' of No. 224 Squadron RAF, on 24 September is not correct as this attack damaged U-763.