German submarine U-1166 was a Type VIIC/41 U-boat of Nazi Germany's Kriegsmarine during World War II.
She was ordered on 14 October 1941, and was laid down on 4 February 1943, at Danziger Werft AG, Danzig, as yard number 138. She was launched on 28 August 1943, and commissioned under the command of Oberleutnant zur See Herbert Wagner on 8 December 1943.
German Type VIIC/41 submarines were preceded by the heavier Type VIIC submarines. U-1166 had a displacement of when at the surface and while submerged. She had a total length of , a pressure hull length of , an overall beam of , a height of , and a draught of . The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of for use while surfaced, two SSW GU 343/38-8 double-acting electric motors producing a total of for use while submerged. She had two shafts and two propellers. The boat was capable of operating at depths of up to .
The submarine had a maximum surface speed of and a maximum submerged speed of . When submerged, the boat could operate for at ; when surfaced, she could travel at . U-1166 was fitted with five torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes or 26 TMA or TMB Naval mines, one SK C/35 naval gun, (220 rounds), one Flak M42 and two C/30 anti-aircraft guns. The boat had a complement of between forty-four and fifty-two.
On 28 July 1944, U-1166 was badly damaged in a torpedo explosion. She was later decommissioned in Kiel on 28 August 1944, and converted to a floating power station. On 3 May 1945, U-1166 was scuttled at the Deutsche Werke shipyard in Kiel off of dry dock No. 2. Her wreck was raised and broken up.