New Mexico class battleships

The New Mexico class battleships were slightly improved versions of the previous Pennsylvania class, with a clipper bow and a more useful arrangement of secondary guns.

New Mexico class battleship bombardments Okinawa
New Mexico class
bombardments Okinawa

The US Navy had wanted to make a break with previous designs, and produce a new type of ship, armed with 16in guns, but the Secretary of the Navy had refused to fund such an ambitious plan, and so the navy had to make do with an improved Pennsylvania class. The main changes were introduced in an attempt to make the ship less 'wet' and to increase the usability of the secondary guns.

This was achieved in two ways, first by giving the ships a 'clipper' bow (making the ship longest at the top of the bow, which then sloped back sharply as at dropped towards the waterline). Second, twelve of the 5in guns were moved from their position in a casemate in the forecastle deck to a new deckhouse position build on top of the forecastle deck. Two more guns were mounted on top of the deckhouse and eight left in their casemates (four forward and four aft). As these ships were being completed the US Navy was finally gaining experience of using their dreadnoughts in combat conditions, operating in the North Sea with the Royal Navy. It soon became clear that the casemate mounted guns were useless in heavy seas, and they were removed from the New Mexico design, leaving them with fourteen 5in guns, all of which were useable.

USS Idaho (BB-42) in Panama Canal, 1945
USS Idaho (BB-42) in Panama Canal, 1945

The New Mexico class also saw the introduction of a new 14in/ 50cal gun, replacing the 14in/ 45cal guns used on earlier battleships. The new guns thus had 70in longer barrels, improving their power. The main guns could also be elevated separately, something that had not been possible on earlier battleships. This made it easier to find the range of a target, as each turret could effectively fire three different ranging shots in a single volley.

Two of the ships used standard geared turbine engines, but the New Mexico was given a turbo-electric drive. These engines were somewhat heavier than the turbines, but were more economical to run and allowed the astern turbines to be removed. The turbo-electric drives were adopted on the Tennessee and Colorado class battleships, and would have been used on the South Dakota class ships if they had ever been built, but they were abandoned after the First World War. The New Mexico was given a geared turbine during a 1920s refit.

The New Mexico class ships were modernized in the early 1930s. Their machinery was replaced with new boilers and geared turbines. The cage masts were removed and two tower bridges built - a large one forward and smaller one aft. Anti-torpedo bulges were added and the gun elevation increased to 30 degrees.

All three ships were part of the Neutrality Patrol in the Atlantic when the Japanese attacked Pearl Harbor, and represented almost half of the available battleship strength of the US Navy. They were used to protect the US west coast early in 1942, and then took part in most of the island invasions in the Pacific, from the Aleutians to the Philippines. 

Displacement (standard)


Displacement (loaded)


Top Speed



8,000nm at 10kts

Armour – belt


 - deck


 - turret faces

18in or 16in

 - turret sides


 - turret top


 - turret rear


 - barbettes


 - coning tower


 - coning tower top





97ft 5in


Twelve 14in guns in four triple turrets
Fourteen 4in guns
Four 3in guns
Two 21in submerged beam torpedo tubes

Crew complement


Ships in Class


USS New Mexico (BB 40)

Stricken 1947

USS Mississippi (BB 41)

Stricken 1956

USS Idaho (BB 42)

Stricken 1947

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How to cite this article: Rickard, J (23 September 2011), New Mexico class battleships ,

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