"A war situation" is precisely when you need this sort of thinking: the modern ethical framework for medical research with interventions is heavily influenced by "The Nuremberg Code". I don't think we need to describe in detail why people thought that code was necessary.

In most of these cases, it is highly unlikely that any significant number of the patients will withhold their consent: so to not ask it is basically saying "we can't be bothered", there's no obvious scientific basis for such a waiver. When patients are incapacitated there are equivalent frameworks which take their personal circumstances into consideration.