Members of the US military have a duty to not follow "manifestly unlawful" orders Army Doctrine 101 https://talent.army.mil/wp-content/uploads/2020/11/ARN20039_ADP-6-22-C1-FINAL-WEB.pdf Of course soldiers might not know what is an unlawful order, but they will know about manifestly unlawful ones. Examples are given in the card they are all given on the Geneva Convention. If your superior ordered you to shoot the prisoner of war, you'd know that's manifestly unlawful. If your superior ordered you to rape women in the village, you'd know that's not only illegal but also immoral. And the point it, if you did these things, you cannot use the excuse of superior orders to determine innocence. At best, its mitigation ie. "yes I raped the prisoners, but the other threatened to kill me if I didn't", might reduce your sentence, but you are still guilty of a war crime. This was the controversy behind My Lai. Calley used the Superior Orders defence, because he believed that order to rape and execute the villagers was legal. In most countries, a Nuremburg defence of "following orders" is not valid. US military law is more vague. Its (superior order defence) allowed, except when the prosecution can show that the defendant knew the order to be illegal. So the example would be that members of the military are instructed, in general, of their rights and obligations under the Geneva Convention; they can refuse orders to work, they don't have to divulge many details about their service, and they probably know that if someone tries to beat information out of them, that person is breaking some law. There are "pesky ROEs" which also help frame for the soldier what they can do, and what they can't do. Not following the ROE doesn't mean you are suddenly a war criminal, but following the ROE is a pretty good start (even if the ROE contains instruction that is legally dubious, you will have a defence that it wasn't obviously illegal to you). Soldiers do get a lot of instruction on the so-called laws of warfare. I was schooled by a warrant officer on the details of the Convention, when I suggested that a bit of kit I designed and fielded could be abandoned with the help of a grenade. A grenade would have scattered a certain banned munition across a field, which would then have to be cleaned up, using a process that might, based on precedence, take 50 years. So soldiers do have a pretty good sense of an illegal order. So they are not obliged to obey all orders, and in fact they are obliged to disobey illegal orders, such as executing civilians, torturing a surrendered prisoners of war, denying medical treatment to fallen combatants, taking hostages, mutilation of prisoners, protecting POWs from public curiousity (ie. the Ukrainians were breaking the Geneva convention by posting on Youtube interviews with Russian POWs). All these things are obvious, because you know these things from the Geneva card.
