On September 12, 1942, U-156 under Kapitänleutnant Werner Hartenstein torpedoed the RMS Laconia, a British troopship, 600 miles south of the Azores. As the ship sank, Hartenstein was horrified to discover she was carrying not just British soldiers but over 1,800 Italian prisoners of war (Germany's allies) and hundreds of Polish civilians, including women and children.
In an extraordinary decision, Hartenstein surfaced, began pulling survivors from the water, and broadcast an uncoded message on open frequencies: he announced his position, pledged not to attack any vessel that came to help, and requested assistance. He draped Red Cross banners across U-156's deck and began towing lifeboats.
Two other German U-boats and an Italian submarine joined the rescue. At one point, over 200 survivors were crammed onto U-156's deck and in its hull, with more in towed lifeboats. Vichy French ships were dispatched from Dakar to assist.
Then, on September 16, an American B-24 Liberator bomber spotted the submarine. Despite the clearly visible Red Cross flags and the lifeboats in tow, the aircraft attacked, dropping bombs and depth charges. U-156 was forced to crash-dive, leaving survivors in the water. Hartenstein managed to pass most of the survivors to the French ships before departing.
The incident had far-reaching consequences. Admiral Dönitz issued the Laconia Order, forbidding U-boat commanders from rescuing survivors—a directive that was controversially used against him at the Nuremberg Trials. The order arguably condemned thousands of future shipwreck survivors to death, turning what had been a common humanitarian practice into a prohibited act.
Of the Laconia's estimated 2,732 passengers and crew, approximately 1,113 survived. Hartenstein and U-156 were sunk with all hands in March 1943.