PACIFIC OCEAN (Sept. 18, 2021) The Arleigh Burke-class guided-missile destroyer USS Mustin (DDG 89) fires its 5-inch gun while underway in the Pacific Ocean, Sept. 18, 2021. Mustin is currently underway in the U.S. 4th Fleet area of responsibility conducting a series of exercises designed to increase interoperability and build capacity among partner nations. (U.S. Navy photo by Mass Communication Specialist 2nd Class James S. Hong)