Once A Marine Shirt. Short-Sleeve Shirts, 100% Cotton Casual Men’s Shirts, Show Your Pride With Our Military Once A Marine Always A Marine Corps – of the United States Marines USMC Shirts Unisex T-Shirts for Men or Women (Large). 100% cotton Preshrunk. Once A Marine Shirt, a Large imprint on the back of the shirt, and a small matching crest on the front left side.