|Ordered||25 Aug 1941|
|Laid down||23 Jan 1943||AG Weser, Bremen (werk 1074)|
|Launched||29 Jul 1943|
|Commissioned||17 Nov 1943||Korvkpt. Walter Pommerehne|
|Successes||No ships sunk or damaged|
Sunk 18 March, 1945 in the North Atlantic north-east of Boston, in position 43.18N, 61.08W, by depth charges from the US destroyer escorts USS Lowe, USS Menges, USS Pride and USS Mosley. 55 dead (all hands lost).
Men lost from U-boats
Unlike many other U-boats, which during their service lost men due to accidents and various other causes, U-866 did not suffer any casualties (we know of) until the time of her loss.