From their website: "The USMC Vietnam Tankers Association is a non-profit fraternal organization (brotherhood) of United States Marines and Navy Corpsmen veterans who served with any of the three Marine Corps tank battalions (1st, 3rd and 5th Tank Battalions) or anti-tank battalions (1st, 3rd and 5th Anti-Tank Battalions) in Vietnam between 1965 and 1970." https://www.usmcvta.org/