Mekong Delta, or?
This 1985 photo of a Columbian marine participating in an amphibious/jungle assault during the joint US/South American Exercise UNITAS XXV, complete with his M1 helmet and M14 rifle, could almost be mistaken for a U.S. Marine in 1965 South Vietnam.
NARA photo DN-ST-85-08732
For reference:
1965: Marines from the 3d Battalion, 4th Marines take cover near Phu Bai Their patrol had just been fired upon by the VC USMC Photo A185701