The 54-caliber (Mk 45) lightweight gun provides surface combatants accurate naval gunfire against fast, highly maneuverable surface targets, air threats and shore targets during amphibious operations aboard the guided missile destroyer. San Jacinto is underway with the USS Harry S. Truman (CVN 75) Battle Group for a Joint Task Force Exercise (JTFEX). U.S. Navy photo by Photographer's Mate 1st Class Michael W. Pendergrass.