USS Idaho (BB-42), a New Mexico-class battleship, was the fourth ship of the United States Navy to be named for the 43rd state. She was the third of three ships of her class. Built by the New York Shipbuilding Corporation of Camden, New Jersey, she was launched in June 1917 and commissioned in March 1919. She was armed with a battery of twelve 14-inch (356 mm) guns in four three-gun turrets, and was protected by heavy armor plate, with her main belt armor being 13.5 inches (343 mm) thick.
Idaho spent most of the 1920s and 1930s in the Pacific Fleet, where she conducted routine training exercises. Like her sister ships, she was modernized in the early 1930s. In mid-1941, before the United States entered World War II, Idaho and her sisters were sent to join the Neutrality Patrols that protected American shipping during the Battle of the Atlantic. After Japan attacked Pearl Harbor on 7 December 1941, Idaho and her sisters were sent to the Pacific, where she supported amphibious operations in the Pacific. She shelled Japanese forces during the Gilbert and Marshall Islands and the Philippines campaigns and the invasions of Peleliu, Iwo Jima, and Okinawa.
Idaho was among the ships present in Tokyo Bay when Japan formally surrendered on 2 September 1945. With the war over, the ship was decommissioned in July 1946. She was sold to ship breakers in November 1947 and subsequently dismantled.
