The German Type IXB submarine was a sub-class of the German Type IX submarine built for Nazi Germany's Kriegsmarine between 1938 and 1940. The U-boats themselves were designed to be fairly large ocean-going submarines. The inspiration for the Type IXB submarine came from the earlier original Type IX submarine, the Type IXA submarine. The design of the IXA was developed to give an increased range, a change which resulted in a slightly heavier overall tonnage. This design was improved even further in the later Type IXC submarines.

German submarine U-103 was a Type IXB U-boat of Nazi Germany's Kriegsmarine that operated during World War II. She was one of the most successful boats in the entire war, sinking 238,944 gross register tons (GRT) of Allied shipping in 11 patrols, in a career lasting more than four years.