This was designed in 1965 following lessons learned from the M1951 Cold Weather System. It didn’t require much fixing, but they added an integral hood, some cuff extenders, velcro, and a rounded collar. This was a staple of the aesthetics of the Vietnam War, its protests, and its support rallies.
This jacket, when worn with its liner, its genuinely good down to at least 30 degrees Fahrenheit when standing static. That makes it good with a liner when moving down to almost 0 degrees.
The shell material is a NyCo polin blend.
The hood is barely a hood and is more of a windproof bit you put on under your helmet or over a knit wool hat to add a little more warmth.