Based on my past postings, part of which can be read below, this following confirmation has been left by a Cryptomundian identifying himself as “VietVet”:

In country, 65-66, 70-71, 71-72.
Rock Ape sightings. Central highlands and up.
Humped jungle in line plt. (squad size 6-10) and of course Recon and LLRPS.

Your sightings were more likely from out in the bush (infantry) and not base camp, better known as (REMF’S).

Sightings limited for reason of proximity and location, not to mention reports.

Example the RTO gets on the horn and our Lt. reports to the commander, “Enemy contact 3 kia’s. NVA or VC?”
“No we killed 3 rock apes.”
“Don’t the damn fools know the difference between the enemy and a bunch of monkeys.”

Looks nice on a sitrat (situation report), doesn’t it?
A lot happens and [is] never reported and/or not considered significant, especially in a war zone.

Yes, they are real; how do I know?
I saw them and I say they are real; big deal, don’t mean nothin’.
VietVet

In the book, Very Crazy GI – Strange but True Stories of the Vietnam War, Vietnam War veteran Kregg P. J. Jorgenson tells of how he had an actual sighting of a short, red-haired, hairy, upright anthropoid, which he says soldiers in Vietnam called a “Rock Ape.” One even was said to be captured in Dak Lak Province in 1971, and in 1974 a North Vietnamese general, Hoang Minh Thao, requested an expedition to find evidence of the creatures, but it was unsuccessful.

Other soldiers, we are told, down through the years, have told of their own Vietnam War era encounters with these cryptids.

Incidents are to be found on the Internet, such as this one here:

All except one was light brown to reddish brown in color, and about 3 1/2 four feet  tall. One dark, almost black, male remained fighting to protect the others retreat and he was flying through the branches and rushing the men with his teeth bared. He was one very brave animal, I’ll tell you that. Michael Kelley

And here:

When Poncho got control of himself, he told me that he had been walking back to the bunker when he noticed a bush that hadn’t been there before. He bent over to see it better and it SNORTED at him and he fired. What he had encountered was the ubiquitous Rock Ape of Vietnam. I would come to learn that they were nearly everywhere, and quite fearless. That is what we had heard near the wire that night.Robert “JungleVet” Baird

Names like “Monkey Mountain” apparently referred not to local monkeys but to the Rock Apes.