RMS Laconia was sunk by a U-boat off the coast of West Africa, which then attempted to rescue the passengers as it was acting under the old prize rules.

RMS Laconia was a Cunard ocean liner, built by Swan, Hunter & Wigham Richardson as a successor of the 1911–1917 RMS Laconia. The new ship was launched on 9 April 1921, and made her maiden voyage on 25 May 1922 from Southampton to New York City. At the outbreak of the Second World War she was converted into an armed merchant cruiser, and later a troopship. She was sunk in the South Atlantic Ocean on 12 September 1942 by U-156. Some estimates of the death toll have suggested that over 1,658 people were killed when the Laconia sank. Hartenstein staged a rescue of the passengers and the crew of Laconia, which involved additional German U-boats and became known as the Laconia incident.

The Laconia incident was a series of events surrounding the sinking of a British passenger ship in the Atlantic Ocean on 12 September 1942, during World War II, and a subsequent aerial attack on German and Italian submarines involved in rescue attempts. RMS Laconia, carrying 2,732 crew, passengers, soldiers, and prisoners of war, was torpedoed and sunk by U-156, a German U-boat, off the West African coast. Operating partly under the dictates of the old prize rules, the U-boat's commander, Korvettenkapitän Werner Hartenstein, immediately commenced rescue operations. U-156 broadcast her position on open radio channels to all Allied powers nearby, and was joined by several other U-boats in the vicinity.

U-boats are naval submarines operated by Germany, including during the First and Second World Wars. The term is an anglicized form of the German word U-Boot, a shortening of Unterseeboot. Austro-Hungarian Navy submarines were also known as U-boats.