Might be worth referencing The Laconia Incident here (Wikipedia is your friend).
Not too well publicised, as it paints several participating combatants in a poor light. In short, 1942, German U-Boat U-156 sank the British liner RMS Laconia, unaware that a substantial number of Italian POWs were on board. As the ship sank the U-Boat commander, Korvettenkapitan Hartenstein, ordered his vessel to surface, assisted the survivors and transmitted an uncoded mayday. Some time later as his and compatriot submarines were actually towing the lifeboats towards land, the flotilla was attaacked by an American B-24 and B-25s, and the U-Boats were forced to escape.
The upshot of this incident was Grand Admiral Doenitz issuing orders forbidding his vessels from such assistance henceforth; the so called Laconia Order. At Nuremburg, Doenitz was indicted on this count as a War Crime, but received no sentence as, it was argued, British and American vessels had implemented identical policies since the beginning of their participation in the War.
(Incidentally, and for the alleviation of confusion, my solicitors (Damidges, Grabbit and Runne) have advised me to make the following declaration;
1. I am unrelated by birth or marriage to any 3rd Reich Grand Admirals.
2. I am unrelated to the namesakes of any dock-bound Type 45 Destroyers beginning with D.
3. I have no business connection to any high street circular-sweet-patisserie franchise).