German submarine U-128 was a Type IXC U-boat of Nazi Germany's Kriegsmarine during World War II. She was sunk 17 May 1943, by American action.
German Type IXC submarines were slightly larger than the original Type IXBs. U-128 had a displacement of when at the surface and while submerged. The U-boat had a total length of , a pressure hull length of , a beam of , a height of , and a draught of . The submarine was powered by two MAN M 9 V 40/46 supercharged four-stroke, nine-cylinder diesel engines producing a total of for use while surfaced, two Siemens-Schuckert 2 GU 345/34 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-128 was fitted with six torpedo tubes (four fitted at the bow and two at the stern), 22 torpedoes, one SK C/32 naval gun, 180 rounds, and a SK C/30 as well as a C/30 anti-aircraft gun. The boat had a complement of forty-eight.
Ordered on 7 August 1939 from DeSchiMAG AG Weser in Bremen, U-128 was laid down on 10 July 1940, launched on 20 February 1941 and commissioned by Kapitänleutnant Ulrich Heyse on 12 May 1941.
The boat was a training vessel in the second flotilla until 30 November 1941 based in Wilhelmshaven. She was then based in Lorient.
During her six completed war patrols, U-128 sank 12 ships, for a total of 83,639 tons. On 1 March 1943 command was transferred to Kptlt. Hermann Steinert, who commanded her until her loss a few months later.
On 17 May 1943, while operating in the South Atlantic near Pernambuco, two Mariner flying boats, PBM 74-P5 and PBM-74-P6 of the US Navy Patrol Squadron VP-74, made U-128 surface with depth charges. Two US Navy destroyers ( and ) also hit her with 5-inch gunfire. The crew opened the submarine's seacocks as they abandoned ship, scuttling the submarine. The final toll was seven dead but there were 47 survivors.