I won't say what I think until others have posted and what Happen on memorial day when I went to see my wife on her resting place.......
As with most things military, so long as you have the paperwork to support it....
1. Formally assigned to a combat unit and in a MOS/TOE slot that requires participation in combat operations.
2. In an area officially designated as a combat zone/area of operations.
Disclaimer: I never was in the service.
To me a combat veteran is somebody that was in combat. IE: bullets flying, bombs dropping.
I know a couple of guys that in the service during Viet Nam but never went to Nam. I do not consider them a "combat veteran" but they could have been. Just depends on where they were deployed to.
I was stationed on a carrier (not aircrew) that flew combat missions into Laos, etc. I do not consider myself a combat vet.
I spent 9 months on a carrier off the coast of N. Vietnam (Yankee Station). We received "hostile fire" pay (and free postage) and I got hazardous duty pay because I worked on the flight deck but I consider my self a Vietnam Veteran, but not a combat veteran. The pilots and aircrew however, were.
The Marines had (still do ?) a Combat Action Badge, the Marine Corps doctrine in the 60s was that every Marine was a rifleman first and back then Marines went through Infantry Training regiment after finishing Boot
Camp. There have been various attempts over the years to introduce a Combat Armor and Combat Artilleryman's badge in the Army, all have been rejected. One Vietnam vet MP told me his platoon regularly accompanied the grunts as POW handlers, they were put in for the CIB-and turned down. Many rear echelon and base camp types said they endured their share of shellings, rocket attacks, sapper attacks but received no recognition. Paratroopers who landed under fire were entitled to wear a star on their wings. IIRC for Vietnam the CIB was awarded only after 30 days in an infantry unit.