I would hazard to guess that the Pentagon as a body has never said, “This war’s a mistake, we gotta get our people out of there before more of them get killed for no good reason.” I’m sure individual generals and whatnot have said it, but not any of the guys speaking as a whole.
I’m cool with that, it’s their job to fight wars, and to support the Commander in Chief. I know that some generals have privately told the President and his top advisors that they would be sticking America’s collective dick in the pencil sharpener by going to war with country A. But you know, when the President and his supporters say, “Our general have advised us that this war is winnable, so we must stay the course” let no one assume this constitutes objective advice. It’s just the Pentagon supporting the Commander in Chief, as it always does in time of war. What ELSE would they say? The Pentagon, by it’s very nature, is not a credible source here.
By 1966, the Pentagon and the DoD was telling LBJ that the Vietnam war was unwinnable without increasing the troop levels significantly. (Basically a doubling.) Not the same advice as “let’s go home”, but given that 1. the troop levels couldn’t be increased for political/economic reasons and 2. everyone knew that Pentagon estimates were always lowballed, it came to the same thing. (And this didn’t even take into account how many decades such troop levels would have to be maintained.)
So from then on, it was a “Peace with Honor” strategy. Cause as much damage as possible in hoping for peace terms that didn’t sound too horrible.
These unnamed Pentagon generals may or may not agree with the people above them, but they have a serious duty to the people below them. I think our military would be completely wrecked if our generals started speaking plainly and openly about this being a lost war, or however one might phrase it. What private first class wants to go out on patrol if a deity-like figure like a four-star general starts telling his troops that we’ve already lost?
So, I agree with the OP. Generals have a responsibility to the troops who serve under them, and they ought to provide frank advice to policymakers while keeping up the morale of our troops. That doesn’t make them objective sources of information. I wouldn’t really have a problem with a former general saying that he opposed going to war – like a more frank version of Powell’s recounting of his “Pottery Barn” comment to Bush.
I think it is more that the U.S. hasn’t been in a situation bad enough for the Pentagon to call for an end. If we were Germany in 1945, the Pentagon would probably push for “peace”(i.e. surrender).
So as a GQ(which this isn’t): No, the Pentagon hasn’t called for “peace”, but I think they would if we were on the brink of annihilation.