Factual error: When Michael Vronsky gets back from his tour he has a full grown beard. The only branch of the service that allows a beard is the Navy, and he was an Army Green Beret. The beard would only have been tolerated if Mike was either not in his Class A uniform or actively performing on a mission, neither of which are the case here. In addition, he's wearing a Black Beret, but his left shoulder patch is the 101st airborne, not Special Forces. Finally, he has six or seven hash marks on his right sleeve. Each hashtag is for 3 years of active duty service.
Factual error: Back from Viet Nam, De Niro is wearing a green beret and he has a 101st Airborne Division patch on the left shoulder of his dress greens. It should be a Special Forces patch.