Donate to the Lead Adventure Forum to keep it alive!
My suggestion would be to go back a few years and look for rules such as; Body Count. Very old and possibly to be found on Ebay. A bit complicated but full of fantastic ideas.https://boardgamegeek.com/boardgame/26766/bodycount-wargames-rules-vietnam-war
Charlie Company from RAFM was, at the time, a fairly innovative game designed for squad and platoon scale sections. It has the great advantage that it can be readily played as a solo game. They still sell it.http://www.rafm.com/charlie/charlie.html
As a slightly off the wall suggestion (and has been discussed elsewhere), The Walking Dead: All Out War might work for a solo or cooperative game (playing as US and allies).