German submarine U-172 was a Type IXC U-boat of Nazi Germany's Kriegsmarine during World War II.

The submarine was powered by two MAN M 9 V 40/46 supercharged four-stroke, nine-cylinder diesel engines producing a total of 4,400 metric horsepower (3,240 kW; 4,340 shp) for use while surfaced, two Siemens-Schuckert 2 GU 345/34 double-acting electric motors producing a total of 1,000 metric horsepower (740 kW; 990 shp) for use while submerged.

Moving to the eastern Caribbean Sea, she sank three more ships, City of Alma, Delfina and Sicilien in early June.

He was landed at Lorient when the submarine returned to base and was transferred, initially to Wilhelmshaven then the POW camp at Milag Nord near Bremen.

That total was boosted with the destruction of the British troopship SS Orcades (23,456 GRT) southwest of Cape Town on 10 October.

She was first struck by two torpedoes, but following a third hit, a skeleton crew, gunners and volunteers from the passengers remained on board to try and save the ship.

Following the sinking of Aldington Court on 31 October, the survivors were only spotted and picked up by City of Christiania when the third officer climbed a lifeboat's mast and waved a shirt.

The only survivor of this attack was Poon Lim, who eked out an existence for 133 days in the South Atlantic on a Carley float, (a type of liferaft).

The true horrors of the Battle of the Atlantic were illustrated when the U-boat sank SS City of Pretoria in mid-Ocean about 320 nmi (590 km; 370 mi) northwest of the Azores on 16 March 1943.

The submarine did not escape unscathed; while attacking convoy RS-3 on 28 March, as one of eight U-boats, she was seriously damaged but still managed to sink Moanda on the 29th.

She was sunk on 13 December, in mid-Atlantic west of the Canary Islands by Grumman TBF Avenger and Grumman F4F Wildcat aircraft from the escort carrier USS Bogue (CVE-9), and the American destroyers George E. Badger (DD-196), Clemson (DD-186), Osmond Ingram (DD-255) and Du Pont (DD-152).

The battle between U-172 and the small armada of ships and aircraft lasted for 27 hours and as many as 200 depth charges were dropped by the destroyers.