German submarine U-640

German submarine U-640 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 30 October 1941 by Blohm & Voss, Hamburg as yard number 616, launched on 23 July 1942 and commissioned on 17 September 1942 under Oberleutnant zur See Karl-Heinz Nagel.

Design
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-640 had a displacement of 769 t when at the surface and 871 t while submerged. She had a total length of 67.10 m, a pressure hull length of 50.50 m, a beam of 6.20 m, a height of 9.60 m, and a draught of 4.74 m. The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of 2800 to 3200 PS for use while surfaced, two Brown, Boveri & Cie GG UB 720/8 double-acting electric motors producing a total of 750 PS for use while submerged. She had two shafts and two 1.23 m propellers. The boat was capable of operating at depths of up to 230 m.

The submarine had a maximum surface speed of 17.7 kn and a maximum submerged speed of 7.6 kn. When submerged, the boat could operate for 80 nmi at 4 kn; when surfaced, she could travel 8500 nmi at 10 kn. U-640 was fitted with five 53.3 cm torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one 8.8 cm SK C/35 naval gun, 220 rounds, and one twin 2 cm C/30 anti-aircraft gun. The boat had a complement of between forty-four and sixty.

Service history
The boat's career began with training at 5th U-boat Flotilla on 17 September 1942, followed by active service on 1 May 1943 as part of the 6th Flotilla.

In 1 patrol she sank no ships.

Wolfpacks
U-640 took part in one wolfpack, namely:
 * Iller (12 – 14 May 1943)

Fate
There are discrepancies between the fate of U-640 and GS U-657, which was sunk in the same vicinity around the same time. Paul Kemp's book attributes the sinking of British freighter Aymeric to U-640, and then subsequently sunk by HMS Swale (K217) on the 17 May 1943, whereas UBoat.net attributes this success and fate to U-657.

Uboat.net states that U-640 was sunk on 14 May 1943 in the Atlantic Ocean in position 60.53333°N, -31.08333°W, by depth charges from a US Catalina of VP-84. All hands were lost.