German submarine U-135 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II.

She was laid down at the Vulkan-Vegesackerwerft in Bremen on 16 September 1940 as yard number 14, launched on 12 June 1941 and commissioned on 16 August with Oberleutnant zur See Friederich-Hermann Praetorius in command.

The submarine was powered by two MAN M 6 V 40/46 four-stroke, six-cylinder supercharged diesel engines producing a total of 2,800 to 3,200 metric horsepower (2,060 to 2,350 kW; 2,760 to 3,160 shp) for use while surfaced, two Brown, Boveri & Cie GG UB 720/8 double-acting electric motors producing a total of 750 metric horsepower (550 kW; 740 shp) for use while submerged.

Her route took her across the North Sea and into the Atlantic Ocean via the passage between the Orkney and Shetland Islands.

As part of wolfpack 'Ziethen',[4][1] she sank Gandia on 22 January 1942 420 nmi (780 km; 480 mi) east of Cape Race, (Newfoundland).

Having departed Brest on 26 April 1942, she sank Fort Qu Appelle on 17 May north of Bermuda.

U-135's sixth patrol was toward Greenland; she was attacked by a British B-24 Liberator of 120 Squadron northeast of Ireland on 8 February 1943.