The New Mexico class was a class of three dreadnought battleships built for the United States Navy in the late 1910s. The class comprised three ships: , the lead ship, , and . Part of the standard series, they were in most respects copies of the s that immediately preceded them, carrying over the same main battery arrangement of twelve guns, but now increased to 50-caliber. They incorporated several other improvements, including a better arrangement of the secondary battery that increased its usability, a clipper bow that improved seakeeping, and an experimental turbo-electric propulsion system adopted on New Mexico. Like the other standard-type battleships, they had a top speed of that allowed the fleet to operate as a tactically homogeneous unit.
All three ships spent the bulk of their peacetime careers in the Pacific Fleet; throughout the 1920s and 1930s, they were involved in numerous Fleet Problems, which were large-scale training exercises that helped develop the doctrine later employed during the Pacific War. By 1941, the three ships were moved to the East Coast to join the Neutrality Patrols that protected American merchant ships from German U-boat attacks during the Battle of the Atlantic. Following the Japanese attack on Pearl Harbor in December, they were quickly transferred back to the Pacific, though they spent most of 1942 escorting convoys off the west coast of the United States. Beginning in mid-1943, they supported amphibious operations during the Aleutian Islands, Gilbert and Marshall Islands, and the Mariana and Palau Islands Campaigns. The Philippines Campaign followed in late 1944, though Mississippi was the only member of the class to participate in the early stages of the campaign, the other vessels being under refit at the time. There, she was present for the Battle of Surigao Strait on 24 October, the last battleship engagement in history.
Mississippi and New Mexico took part in the Invasion of Lingayen Gulf, part of the Philippines Campaign, in early 1945 and both were hit by kamikazes. As they were both under repair, only Idaho participated in the Battle of Iwo Jima, but all three ships were part of the bombardment force for the Battle of Okinawa, where all were damaged by kamikazes. They were present for the occupation of Japan in August and September, thereafter returning to the United States. New Mexico and Idaho were quickly decommissioned and sold for scrap, but Mississippi remained in service, having been converted into a gunnery testing and training ship. In this capacity, her crew experimented with anti-aircraft missiles in the mid-1950s before the ship was sold to ship breakers in 1956.
Design
In the early 1910s, the US Navy began experimenting with guns as other navies began to move to weapons. As development of the new guns progressed, the Navy evaluated a series of proposals for ships incorporating 16-inch guns. The first was a ten-gun ship with five twin-gun turrets that also included improved armor compared to earlier battleships. Additionally, the secondary battery was increased from the standard US armament of guns to weapons. Another smaller version with eight 16-inch guns was also suggested, along with a design mounting the then-standard gun. As work on the new design progressed, the cost of the vessels increased significantly. Compared to the cost of a 14-inch-gunned ship—$12 million—the eight-gun ship was estimated to cost $16.5 million, while the price for the ten-gun ship rose to $19 million.
Even before trials of the new guns had been completed, Rear Admiral Joseph Strauss, then the Chief of the Bureau of Ordnance (BuOrd), argued in 1913 that the 16-inch gun was not worth pursuing; he argued that at the expected battle ranges of the day, the 14-inch gun was capable of penetrating heavy armor plate just as effectively and that a ship carrying twelve of those guns had a much better chance of hitting than a ship with eight 16-inch guns. The General Board concurred and instructed the designers to work on the 14-inch ship. Existing turrets for those guns used a single recoil slide for all three guns, which caused concern that a single hit could jam it and thus disable all three guns. Strauss accordingly suggested that the designers at the Bureau of Construction and Repair, under Chief Constructor Richard Watt, incorporate independent slides.
The design staff submitted two proposals on 21 November 1913: a version and a variant. The first incorporated a secondary battery of twenty 6-inch guns, while the smaller one retained twenty-two of the standard 5-inch guns. Weight savings were also achieved by reducing the thickness of the barbette and belt armor by an inch, and reducing fuel capacity. The General Board preferred the larger of the two, citing the heavier armor as needed to defeat the latest 15-inch guns being adopted in foreign battleships and the stronger secondary battery, which they viewed as necessary to ward off long-range torpedo attacks by destroyers. Secretary of the Navy Josephus Daniels disagreed, and on 3 January 1914, rejected the design owing to its higher cost. Instead, he ordered the Navy to accept a repeat of the preceding , which might be fitted with separate slides for the main guns.
Work on the design continued through the year; the designers were concerned that earlier battleships were too "wet" forward, leading to the adoption of a clipper bow to reduce the tendency to ship water in heavy seas. Additionally, experience with existing ships had revealed that the secondary battery, mounted in casemates in the forecastle deck, were effectively unusable in rough sea conditions. The designers therefore moved eighteen of the guns a deck higher and further aft, where they would be less prone to being washed out. Weight savings elsewhere allowed the designers to strengthen the main deck and the transverse bulkhead at either end of the belt. Daniels approved these changes on 2 July, and the following month, BuOrd suggested a newly developed 50-caliber version of 14-inch gun be used, which Watt authorized in September. The longer gun produced a higher muzzle velocity, which allowed the shells to penetrate an additional of armor at . By this time, work on the design stopped, as bids for the contracts were to be submitted starting on 6 October.
Despite the fact that the offer period had opened, one more major change to the design was made. At the time, the standard propulsion system for warships relied on steam turbines to turn propeller shafts, though turbines operated most efficiently at high speed, while the propellers generated thrust most effectively at relatively low speed. One solution to this problem was turbo-electric transmission, which used the turbines to generate electric power that in turn powered electric motors that drove the screws. The Bureau of Steam Engineering (BuEng) recommended the new system on 17 October, pointing out that it would have many advantages over traditional direct-drive systems, including greater fuel economy and lighter and smaller machinery, which could be used to shorten the armored box that protected the ships' vitals. Also, since the turbines would only need to spin in one direction, simpler machinery without reverse gears could be used. Daniels was convinced, and he approved the change for New Mexico on 10 November. Since this was an unproven technology, the other two members of the class received geared turbine systems.
Congress authorized two ships for the class— and —but in mid-1914, the two pre-dreadnoughts were sold to the Greek Navy, and the US Navy was able to use the funds generated by their sale to fund a third member of the class, .
General characteristics and machinery
The ships of the New Mexico class were part of the standard series that began with the ; they featured similar characteristics, including speed, armor, armament, and the use of fuel oil rather than coal. They were designed as such to create a battle fleet of tactically homogeneous ships that would simplify command and control. They were long at the waterline and long overall. They had a beam of and a draft of . They displaced as designed and up to at full combat load. Their hulls featured a long forecastle deck that stepped down to main deck level at the main mast. As built, the ships were fitted with two cage masts with spotting tops for the main-gun battery.
Their crew numbered 58 officers and 1,026 enlisted men. Over the course of their careers, their crews expanded significantly as equipment was added. After their early 1930s refit, their crew numbered 82 officers and 1,371 enlisted, and by 1945, wartime improvements brought the crews to 129 officers and 1,850 enlisted. They carried a number of smaller boats for utility purposes while in harbor, as well as to assist with rescue efforts at sea. These included a number of motor launches of various lengths and motor whaleboats.
All three ships were powered by four Curtis turbines, with steam provided by nine oil-fired Babcock & Wilcox boilers. New Mexicos turbines were used to power electrical motors that drove the screw propellers; her system was rated for . The latter two ships, used reduction geared cruising turbines, which could be clutched into the high-pressure turbines to improve fuel economy at low speeds. These were rated at . All three vessels were rated for a top speed of . Though the turbo-electric system was effective and it was repeated in the two following classes, the Navy ultimately decided that the system was too heavy and occupied too much space in the hull, and later ships reverted to traditional turbine propulsion.
The ships had storage capacity for of fuel oil for the boilers, though additional spaces in the hull could be used to increase capacity to , which provided a cruising range of at a speed of . As speed increased, their range decreased significantly: at , they could steam for , and at , their range fell to . Moreover, these figures were assuming the vessels had clean hulls free of marine growth that would inhibit their hydrodynamic efficiency. In service conditions where biofouling added drag to the hulls, their ranges were reduced even further to and , respectively.
Armament
The ships were armed with a main battery of twelve /50 caliber Mark IV guns in four, three-gun turrets on the centerline, placed in two superfiring pairs forward and aft of the superstructure. Unlike earlier American battleships with triple turrets, these mounts were true three-gun turrets, in that each barrel could elevate independently. They fired a shell with a bursting charge. The guns had a muzzle velocity of . Early in their careers, the New Mexicos and the Tennessee class experienced excessive dispersion of shot. After extensive testing, it was eventually discovered to have been caused by overly lengthy chambers, which allowed a gap between the shell and the propellant charges. The problem was eventually corrected with the Mark VII gun. The guns were supplied with 100 shells each and they were capable of a rate of fire of about one salvo per minute, as demonstrated by extensive testing with Idaho in October 1942.