: My recollection is that the "Execute unrestricted submarine warfare" order was considered justified by the Americans on two grounds. The first was that the Japanese had shown contempt for international law by starting the war with a surprise attack, in violation of the Hague Conventions. The second justification offered was that it was lawful retaliation for unrestricted submarine warfare on the part of the Japanese, who had sunk Cynthia Olson off Hawaii almost simultaneously with the opening of the Pearl Harbor attack. Accounts of the sinking are at odds with each other, but there were allegations the crew were machine gunned after abandoning ship. I don't have my copy of Blair handy, but this is  discussed by Roscoe (which I don't have my own copy of.) If we're going to state in the intro that the Allied submarine campaign appeared to violate international law, it seems only fair (e.g. NPOV) to mention the justifications offered for it.