U-156 (Type IXC, foreground) and U-507 (Type IXC, background) at sea during the transfer of survivors from the sunken British military transport RMS Laconia. Photo taken by an officer of U-156, Oberleutenant zur See Leopold Schuhmacher. The Laconia (displacement - 19,695 brt) was torpedoed by two torpedoes from U-156 at 22:07 local time on 12 Sep 1942 at the point with coordinates 05.05S, 11.38W (about 360 miles northeast of Ascension Island in the South Atlantic), having on board 2,741 people: a crew of 136 people, 80 civilians, 268 passengers and about 1,800 Italian prisoners, accompanied by 160 Polish soldiers. Lakonia sank after 1 hour 16 minutes at 23:23. Killed were 97 crew sailors, 133 passengers, 1,394 Italian prisoners and 33 Polish soldiers, the remaining 1,084 people (including 415 Italian prisoners) were in the water.
The commander of U-156, Korvettenkapitän Werner Hartenstein, after agreement with the headquarters (the original text of the radiogram is Versenkt von Hartenstein Brite "Laconia". Marinequadrat FF 7721 310 Grad. Leider mit 1500 italienischen Kriegsgefangenen. Bisher 90 gefischt. 157 Passat 3, erbitte Befehle) began a rescue operation, lifting about 200 people to the upper deck of the boat and about 200 more were in towed lifeboats.
On 13 September at 06:00 a.m., the U-156 broadcasted a clear message that it would not attack any rescue ship if it was not itself attacked. (Original text – If any ship will assist the ship-wrecked ‘Laconia’-crew, I will not attack providing I am not being attacked by ship or air forces. I picked up 193 men. 4, 53 South, 11, 26 West – German submarine).
On the morning of 15 September, German submarines U-506 and U-507 and the Italian Capellini arrived to help U-156. On 16 September at 11:25 am, a cluster of German submarines and people in the water was discovered by an American Consolidated B-24 Liberator bomber from the air base on Ascension Island, the pilot of which, Lieutenant James D. Harden, after receiving an order from the base at 12:32, made an attack. All three submarines hastily plunged below the water level, leaving hundreds of people in the water. Between 17 and 20 September 1942, the remaining approximately 900 people were taken aboard by three ships from Vichy France and landed at various African ports. A small part of the Italian prisoners remained aboard these three German submarines.
This incident was the basis for the issuance on 17 September 1942 of the order Triton Zero (Laconia-Befehl/Order Laconia) to all Kriegsmarine submarine commanders, forbidding any attempts to rescue the crews of sunken ships, that is, to catch the drowning, transfer them to lifeboats, return inverted boats to normal position, provide food and water to victims.