At 21.53 hours on 3 March 1943, U-43 fired a spread of three torpedoes at steamer of the Dunedin Star type, which sank in two minutes after being hit by all three torpedoes. But it later became clear that they had by mistake sunk the blockade runner Doggerbank (KptLt Paul Schneidewind), which was several days ahead of her scheduled arrival.

On board were many crew members of the German supply tanker Uckermark and the raider Thor which had been destroyed in an accident in Yokohama, Japan on 30 Nov 1942. The U-boat had observed that five lifeboats were launched and even tried to question some of the survivors, but it was impossible to understand them because they could not get closer due to the darkness and left. One of the boats was found by the Spanish motor tanker Campoamor on 29 March, but only one man was still alive, taken aboard and brought to Aruba. Fritz Kürt later reported that there had been 15 survivors in his boat but only six managed to get aboard again when it capsized, including the master. They were in a desperate situation without water and food and Schneidewind committed suicide after shooting four of his crew at their explicit request.