On March 2, 1940 U-123 was launched at AG Wesser in Bremen, Germany. For her crews she was a very lucky boat, for the Allies this was not so. Her first patrol started in Sept. of 1940, under the command of Kapitänleutnant Karl-Heinz Moehle. He sank six ships during this patrol. He would take U-123 on three more patrols and sink ten more ships.

On May 19, 1941 Kapitänleutnant Reinhard Hardegen took command, he sailed her on four patrols sinking twenty-one ships. Her third and final commander was Oberleutnant zur See Horst von Schroeter, during his four patrols he racked up another seven ships. In total U-123 sank over 220,000 tons of shipping.

All three of her commanding officers were awarded the Ritterkreuz des Eisernen Kreuz (Knight's Cross of the Iron Cross), Hardegen was also awarded the Eichenlaub (Oak Leaves) to his Ritterkreuz. All three men survived the war as did U-123, she was scuttled at Lorient, France in June of 1944, was later raised and renamed Blaison Q-165 by the French who retained the boat until 1959.

One other note, as of Sept. 2012 Hardegen, her second commander, was still alive and well living in Bremen, Germany. At 99 years old, he is perhaps the only U-Boat commander still living.