German submarine U-123 was a Type IXB U-boat of Nazi Germany's Kriegsmarine that operated 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.

Her route took her across the North Sea, through the gap between the Faroe and Shetland Islands and into the Atlantic Ocean west of Ireland.

She sank six ships in October, including Shekatika which was hit with no less than five torpedoes before she went to the bottom east southeast of Rockall.

On her return to Lorient, U-123's war diary (KTB) was altered on the order of U-boat headquarters (BdU).

Despite criss-crossing the Atlantic, U-123 found the pickings rather thin, she did manage to damage the armed merchant cruiser (AMC) HMS Aurania on 21 October 1941 and take one crewman prisoner.

She began by sinking the cargo ship Cyclops about 125 nmi (232 km; 144 mi) southeast of Cape Sable, Nova Scotia on the 12th.

Moving down the coast, she sank Norness, Coimbra, Octavian , Norvana, City of Atlanta and the Latvian Ciltvaira.

In a reference to American unpreparedness, he commented after sinking Norvana: "These are some pretty buoys we are leaving for the Yankees in the harbor approaches as replacement for the lightships."

She also had a lucky escape on 19 January when Kosmos II (headed by Captain Einar Gleditsch from Sandefjord Norway) tried to ram the boat off Oregon Inlet.

The U-boat escaped when the recalcitrant power plant was restarted at the last minute and flares were fired at the larger vessel's bridge.

By now out of torpedoes and in the case of Pan Norway, the boat used the last of her deck gun ammunition and 37 mm AA weapon to destroy the Norwegian vessel.

The U-boat then encountered a Greek ship, the Mount Aetna, under a Swiss charter, which was directed to the survivors.

[5] The boat's second Paukenschlag mission was also successful – sinking Muskogee and Empire Steel on 22 and 23 March 1942 near Bermuda before moving closer to the US east coast.

The U-boat moved closer, at which point Atik dropped her concealment and opened fire with all weapons.

A 20 mm round detonated in his right thigh, ripped open the flesh from the hip joint to the knee and partially removed it.

The boat proceeded to sink or damage another eight ships; many of them resting on the sea bed in the shallow water with parts of their hulls above the surface.

Another victim was Alcoa Guide, engaged at the relatively close range of 400 m (440 yd) by the deck gun, (U-123 had run out of torpedoes), on 17 April.

The boat then returned to Lorient on 2 May and proceeded to steam to Bergen in Norway before carrying out a series of short journeys to Kristiansand, Aarhus, Kiel and Stettin.

She sank the Spanish-registered motor ship Castillo Montealegre on 8 April 1943 west of Conakry, French Guinea.

[10] U-123 was also successful against a British submarine, HMS P-615 100 nmi (190 km; 120 mi) southwest of Freetown in Sierra Leone on 18 April.

The crew (minus 2 firemen who were killed by the first torpedo) survived, after sailing to the Liberian coast in the one remaining lifeboat.

Von Schroeter promised to send relevant photographs to Lawson a year after the war had ended – and did.

[11] U-123 was depth charged off Cape Finisterre (northwest Spain), by Allied escort vessels on approximately 25 August 1943.

Bonnett of the Royal Canadian Air Force, was armed with a 6-pounder (57 mm) Molins gun and this was the first attack on a U-boat with one of these weapons.