Was an avid hunter as a kid and joined the Marines in 1967. He served in the U.S. Marine Corps during Vietnam and holds the record for number of confirmed kills for Marine snipers, exceeding that of legendary Marine sniper Carlos Hathcock. In just 16 months he killed 103 enemies and another 216 kills were listed as probable’s by the military, only because it was too risky at the time to search the bodies for documents. When he left the Marines he told no-one of his of his role during the conflict and only a few fellow Marines knew of his assignments. It was nearly 20 years before somebody wrote a book detailing his amazing skills as a sniper. Mawhinney came out of anonymity because of this and became a lecturer in sniper schools. He was once quoted saying “it was the ultimate hunting trip: a man hunting another man who was hunting me. Don’t talk to me about hunting lions or elephants; they don’t fight back with rifles and scopes. I just loved it. I ate it up.”

A routinely deadly shot from distances between 300 – 800 yards, Mawhinney had confirmed kills of over 1000 yards, making him one of the greatest snipers of the Vietnam war.