Filming "U-156" off the coast of Cape Town with a floating U-Boat prop
Apparently (with thanks to @alexjs for these two links) this is "U-156" being filmed in conjunction with the BBC. It depicts the 'Laconia Incident' from World War 2 - according to the always-reliable Wikipedia:
In late 1942, a German U-Boat sunk the British troopship Laconia carrying 1800 Italian POWs off the coast of West Africa. Then realising who the passengers were, started rescue operations flying the Red Cross flag. A US Army Air Corp bomber flying out of a secret South Atlantic airbase (Ascension Island) attacked the u-boat which was flying a Red Cross flag. The u-boat abandoned the rescue effort and left the survivors drift to Africa. Over half the survivors died before reaching Africa. This incident led to German Admiral Dönitz to issue the Triton Null Order which came to be known as the Laconia Order; which expressly forbade submarine commanders to rescue survivors from torpedoed ships. The US Navy used that order as justification for a similar order in the Pacific.
