ATLANTIC OCEAN (April 5, 2021) Chief Gunner's Mate Nickolas Walker, right, assigned to the Harpers Ferry-class dock landing ship USS Carter Hall (LSD 50), gives training on the use of the acoustic defense countermeasure (ADC), April 5, 2021. Carter Hall is operating in the Atlantic Ocean with Amphibious Squadron 4 and the 24th Marine Expeditionary Unit (24th MEU) as part of the Iwo Jima Amphibious Ready Group. (U.S. Navy photo by Mass Communication Specialist Seaman Sawyer Connally)