The Type IX U-boat was designed by Nazi Germany's Kriegsmarine in 1935 and 1936 as a large ocean-going submarine for sustained operations far from the home support facilities.

Type IX boats were briefly used for patrols off the eastern United States in an attempt to disrupt the stream of troops and supplies bound for Europe.

These long range boats were frequently equipped with Focke-Achgelis Fa 330 rotor kite towed rotary-wing aircraft.

Notable IXB boats included U-123 commanded by Reinhard Hardegen, which opened up the attack in the US waters in early 1942 known as Operation Drumbeat, U-156, which was bombed by a US aircraft while flying a Red Cross-flag and rescuing survivors of a torpedoed ship (Laconia incident), and U-107 operating off Freetown, Sierra Leone under the command of Günter Hessler, which had the most successful single mission of the war ever with close to 100,000 GRT sunk.

The Type IXC was a further refinement of the class with storage for an additional 43 tonnes of fuel, increasing the boat's range.

U-505 survives at the Museum of Science and Industry in Chicago, and was completely renovated after being moved in 2004 to a purpose-built indoor berth.

[6] DeSchiMAG AG Weser and Seebeckwerft of Bremen, and Deutsche Werft of Hamburg built 54 Type IXC submarines.

[7] DeSchiMAG AG Weser and Seebeckwerft of Bremen, and Deutsche Werft of Hamburg, built 87 of this type.