The New Mexico class further improved on the basic design introduced three years earlier with the Nevada class. The twelve-gun main battery of the preceding Pennsylvania class was retained, but with longer 14"/50 guns in improved triple turrets. Hull design was also upgraded, with a "clipper" bow for better seakeeping, and one ship was fitted with a new propulsion system, in which steam turbines turned electrical generators and the ship's propellers were driven by electric motors. Though eight secondary battery guns were located in very wet bow and stern positions and were soon removed, the rest of the ships' five-inch guns were mounted in the superstructure, a great improvement over the earlier arrangements.

Completed during and soon after the First World War, the New Mexico class were active members of the Battle Fleet during the decades between the World Wars. All were rebuilt in 1931-34, receiving entirely new superstructures, modern controls for their guns, new engines and improved protection against air and surface attack. Anti-torpedo "bulges" increased their width to 106" 3" and displacement went up by a thousand tons or more.

In order to counter the German threat, these ships were transferred from the Pacific to the Atlantic in 1941, leaving the Pacific Fleet inferior in battleship strength to the Japanese Navy. Sent back to the Pacific after the Pearl Harbor Raid devastated the Pacific Fleet's battle line, they were active in the war with Japan until final victory was achieved in August 1945. Their heavy guns provided vital assistance to the many amphibious invasions that marked the Pacific conflict, and Mississippi took part in the Battle of Surigao Strait, the last time in history that battleships fought each other. New Mexico and Idaho were disposed of soon after the War ended, but Mississippi was converted to a training and weapons trials ship and served for another decade. The Navy's first generation of ship-launched guided missiles, the replacements for most of the guns that had long been the focus of her career, first went to sea aboard this old former battleship.

The New Mexico class numbered three ships, all built on the east coast:


New Mexico (BB-40), built by the New York Navy Yard, Brooklyn, New York. Keel laid in October 1915; launched in April 1917; completed in May 1918.

Mississippi (BB-41), built by the Newport News Shipbuilding & Dry Dock Company, Newport News, Virginia. Keel laid in April 1915; launched in January 1917; completed in December 1917.

Idaho (BB-42), built by the New York Shipbuilding Company, Camden, New Jersey. Keel laid in January 1915; launched in June 1917; completed in March 1919.

New Mexico class "as-built" design characteristics:


Displacement: 32,000 tons (normal)

Dimensions: 624' (length overall); 97' 5" (extreme beam)

Powerplant: 27,500 horsepower turbines with electric drive in New Mexico, 32,000 horsepower geared turbines in the other two ships. All had four propellers and a 21 knot maximum speed

Armament (Main Battery): Twelve 14"/50 guns in four triple turrets

Armament (Secondary Battery): Twenty-two 5"/51 guns in single casemate mountings (eleven guns on each side of the ship); soon reduced to fourteen 5"/51 guns. When modernized in the 1930s, two more 5"/51 guns were removed and eight 5"/25 anti-aircraft guns were added.