Yeah, it’s how blatantly illegal it is.

With illegal things, there are always going to be lawyers who will bend over backwards and contort all the facts to try to make it seem legal. John Yoo was famous for doing that to justify literal torture. And not only did he get away with that, he’s now a law professor at Berkeley. So, even if it’s pretty obvious that attacking random boats on allegations of drug trafficking is illegal, it’s illegal in a way that would be difficult to prove in a court of law. In the court of public opinion it’s obvious, 95% of the world would say that it’s absolutely obvious, and even 67% of the US would agree. But, you get a creep like John Yoo in front of a GOP judge and who knows what might happen.

But, in this case they did the thing that the actual Department of Defense’s Law of War Manual (2023) gives as an example of something that would obviously be illegal:

18.3.2.1 Clearly Illegal Orders to Commit Law of War Violations. The requirement to refuse to comply with orders to commit law of war violations applies to orders to perform conduct that is clearly illegal or orders that the subordinate knows, in fact, are illegal. For example, orders to fire upon the shipwrecked would be clearly illegal.

And that example has a footnote with both a legal case, and with an explanation:

Judgement in Case of Lieutenants Dithmar and Boldt, Hospital Ship “Llandovery Castle” (Second Criminal Senate of the Imperial Court of Justice, Germany, Jul. 16, 1921), reprinted in 16 AJIL, 708, 721-22 (1922) (“It is certainly to be urged in favor of the military subordinates, that they are under no obligation to question the order of their superior officer, and they can count upon its legality. But no such confidence can be held to exist, if such an order is universally known to everybody, including also the accused, to be without any doubt whatever against the law. This happens only in rare and exceptional cases. But this case was precisely one of them, for in the present instance, it was perfectly clear to the accused that killing defenceless people in the life-boats could be nothing else but a breach of the law. As naval officers by profession they were well aware, as the naval expert Saalwiachter has strikingly stated, that one is not legally authorized to kill defenceless people. They well knew that this was the case here. They quickly found out the facts by questioning the occupants in the boats when these were stopped. They could only have gathered, from the order given by Patzig, that he wished to make use of his subordinates to carry out a breach of the law. They should, therefore, have refused to obey.”).

This is so obviously against the law that they used it as an example of an illegal order. They also clearly identified the precedent. Then they spent more text in the footnote than in the paragraph itself, carefully explaining that there are some things that are just so obviously illegal that a member of the military can’t pretend they didn’t know it was a crime, and that shooting shipwrecked sailors is so obviously one of those that no sailor could ever claim they didn’t know the order was illegal.