“Even if it was ALL high explosive shells, the U-boats were NOT to be torpedoing passenger liners and they had promised not to do so in any event”. ....................HMMMM? Once they take ammo on board, are they still a passenger liner? Passenger liners probably have rules to follow too. Was there ammo on board? Yes, and previous dives have shown it. Where they warned before departure? Yes, in the NYT if I remember correctly. The owners of the liner put their passengers at risk knowing that they were transporting war supplies (ammo).
Missing the point: it’s all after the fact, even if “true,” which I doubt. The U-Boat captain THOUGHT he was torpedoing a passenger ship, period.