|Ordered:||20 January 1941|
|Builder:||DeSchiMAG AG Weser, Bremen|
|Laid down:||6 April 1942|
|Launched:||14 November 1942|
|Commissioned:||1 March 1943|
|Fate:||sunk in North Atlantic, 6 November 1943 at Coordinates: |
|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|
|Commanders:||Kptlt. Wolfgang Heller|
U-842 was ordered in January 1941 from DeSchiMAG AG Weser in Bremen under the yard number 1048. Her keel was laid down on 6 April 1942 and the U-boat was launched on 14 November the same year. She was commissioned into service under the command of Kapitänleutnant Wolfgang Heller (Crew 30) in 4th U-boat Flotilla on 1 March 1943.
German Type IXC/40 submarines were slightly larger than the original Type IXCs. U-842 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-842 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.
Transferred to the 2nd U-boat Flotilla, U-842 left Kiel on 14 September 1943 for Bergen where she arrived three days later. On 5 October 1943. U-842 set out for operations in the North Atlantic, where she joined operations against convoy ONS 20. The U-boat escaped an attack by one of the escorts, HMS Bazely (K311) on 17 October unscathed, joining group Siegfried operating against convoy HX 262 on 23 October, and group Siegfried 3 on 26 October. In the final days of October, she was part of group Jahn off Newfoundland. In early November U-842 was among the U-boats of group Tirpitz attacking convoy HX 264, when she was spotted and attacked by an aircraft in the early afternoon of 6 November 1943. Second Support Group, consisting of Wild Goose, Magpie, and Starling, attacked the U-boat two hours later, and after more than one hour, U-842 was sunk by depth charges from Wild Goose, there were no survivors.