|Ordered||20 Jan 1941|
|Laid down||1 Dec 1941||Blohm & Voss, Hamburg (werk 620)|
|Launched||20 Aug 1942|
|Commissioned||15 Oct 1942||Oblt. Kurt Jensen|
|Successes||No ships sunk or damaged|
Left Bergen, Norway on 18 March, 1943.
Sunk 7 April, 1943 in the North Sea north-west of Narvik, Norway, in position 69.38N, 05.40W, by torpedoes from the British submarine HMS Tuna. 45 dead (all hands lost).
U-644 operated with the following Wolfpacks during its career:
Eisbär (27 Mar 1943 - 7 Apr 1943)
Men lost from U-boats
Unlike many other U-boats, which during their service lost men due to accidents and various other causes, U-644 did not suffer any casualties (we know of) until the time of her loss.