First patrol

U-126 opened her account by damaging the British Canadian Star about 650 nmi (1,200 km; 750 mi) west of Lands End on 20 July 1941. She had missed with torpedoes and decided to use her guns instead, but accurate return fire from the merchantman (many merchant ships had some form of defensive armament fitted), drove her off before she could finish the job. A week later, things improved when she sank Erato on 27 July, west of northwest Spain. She used her deck gun again to sink the schooner Robert Max on 4 August east of the Azores. She sank the Yugoslavian Sud using the deck gun once more, but in conjunction with the Italian submarine Marconi on 14 August northeast of the Azores.

Second patrol

The boat was rewarded with two sinkings on 10 October 1941 northeast of the Cape Verde islands; Nailsea Manor was carrying HMS LCT-102 as deck cargo when she was attacked. U-126 also sank Lehigh about 82 nmi (152 km; 94 mi) off Freetown, Sierra Leone, on the 19th and Peru on 13 November, southwest of Cape Palmas (Liberia).

She assisted survivors from the German commerce raider Atlantis on the 22nd.^[3]

Third patrol

The boat was also successful in early 1942 as part of Operation Drumbeat (Paukenschlag),^[4] the German assault on merchant shipping along the US coast. She sank many vessels, beginning with Gunny on 2 March about 200 nmi (370 km; 230 mi) south of the Bermudas and finished with Olga on the 12th. One ship that did not sink was Colabee. She was attacked on the 13th about 10 nmi (19 km; 12 mi) off Cape Guajaba, Cuba. The ship ran aground after being torpedoed and abandoned with her engines still running. She was salvaged, repaired and returned to service.

Fourth patrol

There was drama after the sinking of the Norwegian tanker Høegh Giant on 3 June 1942 about 400 nmi (740 km; 460 mi) east of Guyana. The ship's master was questioned by the German sailors, but when he did not understand what was being said, the Germans fired over a lifeboat, wounding one man.^[5]

Other vessels were attacked in the area of the Caribbean and the West Indies, using torpedoes and the deck gun.

Fifth patrol

Patrol number five was the boat's longest – 111 days. The voyage took the submarine to west Africa. On 1 November 1942, she sank the Liberty ship George Thatcher about 100 nmi (190 km; 120 mi) from the coast at Gabon. She was also successful in sinking New Toronto on the fifth 24 nmi (44 km; 28 mi) from Kotonou; her cargo included 75 live cows.

Sixth patrol and loss

One of U-126's victims on this patrol was Flora MacDonald, which was torpedoed on 30 May 1943 south of Freetown in Sierra Leone. The ship did not sink, but after being beached and the cargo salvaged, she burned for 16 days and was subsequently declared a total loss. The U-boat also hit Standella on 2 June. The submarine was attacked by an aircraft (the source does not give the type), off Freetown on the 15th.

The boat was sunk by a Vickers Wellington of No. 172 Squadron RAF, on 3 July 1943, off Cape Ortegal, Spain. There were no survivors from the 55 man crew.^[1][6]