German submarine U-866

German submarine U-866 was a Type IXC/40 U-boat of Nazi Germany's Kriegsmarine built for service during the Second World War. She was ordered on 25 August 1941, laid down in Bremen, Germany on 23 January 1943 and launched on 29 July 1943. She had one patrol.

Design
German Type IXC/40 submarines were slightly larger than the original Type IXCs. U-866 had a displacement of 1144 t when at the surface and 1257 t while submerged. The U-boat had a total length of 76.76 m, a pressure hull length of 58.75 m, a beam of 6.86 m, a height of 9.60 m, and a draught of 4.67 m. The submarine was powered by two MAN M 9 V 40/46 supercharged four-stroke, nine-cylinder diesel engines producing a total of 4400 PS for use while surfaced, two Siemens-Schuckert 2 GU 345/34 double-acting electric motors producing a total of 1000 shp for use while submerged. She had two shafts and two 1.92 m propellers. The boat was capable of operating at depths of up to 230 m.

The submarine had a maximum surface speed of 18.3 kn and a maximum submerged speed of 7.3 kn. When submerged, the boat could operate for 63 nmi at 4 kn; when surfaced, she could travel 13850 nmi at 10 kn. U-866 was fitted with six 53.3 cm torpedo tubes (four fitted at the bow and two at the stern), 22 torpedoes, one 10.5 cm SK C/32 naval gun, 180 rounds, and a 3.7 cm Flak M42 as well as two twin 2 cm C/30 anti-aircraft guns. The boat had a complement of forty-eight.

Service history
Her commander from 17 November 1943 until December 1944 was Korvettenkapitän Walter Pommerehne, followed by Oberleutnant zur See Peter Rogowsky, who commanded her from December 1944 until 18 March 1945.

While under command of Rogowsky, on 18 March, USS Lowe (DE-325) acquired U-866 on sonar and commenced a hedgehog attack. This attack missed the U-boat, which then settled on the ocean floor, attempting to hide from the attacking surface ships. Unfortunately for the U-boat, the seabed in the area was ideal for the surface ship's sonar and USS Lowe, USS Menges (DE-320), USS Mosley (DE-321), and USS Pride (DE-323), all destroyer escorts, continued to attack with depth charges, until the U-boat was judged destroyed.

She did not sink or damage any ships while on patrol.