BB-40 New Mexico Class
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.
The New Mexico class numbered three ships, all built on the east coast. 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. Twenty-five percent of the first line battleships and forty-three per cent of the second line battleships in commission in the United States Navy on 01 July 1921, were built hy New York Shipbuilding Corporation, in addition to various other warships. USS Idaho, ranking as the most powerful type when she was delivered by the yard in March, 1919, is a notable example of the great line of fighting ships built and under construction at this plant. In the manoeuvres of the Pacific Fleet in the spring of 1920, the Idaho added to "Gunning and Engineering Supremacy" the speed record for the battleships of the fleet, averaging 21.6 knots. The Idaho has a displacement of 34,759 tons.
In the earlier stages of turbine development, much opposition was expressed by the proponents of reciprocating machinery. With the increasing efficiency of turbine propulsion, however, this opposition has practically disappeared, and the manifold advantages due to turbine installations in warships are such that, for that class of vessels, turbine machinery has largely superseded the reciprocating engine. The introduction of the gear drive instead of direct-acting turbines has had much to do with the increasing favor with which turbine propulsion has ibcen regarded. The introduction of the gear drive has permitted a reduction in the revolutions of the screw and the use of greater blade areas with smaller number of revolutions of propellers. This has contributed greatly to the efficiency of this type of propulsive mechanism. There is also now being steadily developed the internal combustion engine. This type of propelling machinery has not, however, had extensive use in naval vessels, other than submarines. On the other hand, the use of electrically-driven propelling machinery has made rapid advances, even for installation on capital ships. This advance has been so notable that it seems appropriate to refer in greater detail to the results obtained through the installation of this type of propelling machinery on one of the most recently built battleships of the United States navy and its prospective installation on the very latest battleships and battle cruisers designed for that navy.
Practical use of the electric drive for the main propelling machinery of capital ships had not been made in of capital ships in navies other than that of the United States up to the time of the New Mexico, although this type of machinery was, of course, under consideration. In the United States navy, however, its installation was attended with conspicuous success. It was first tried on a large scale on the naval collier Jupiter. After most exhaustive tests on this vessel, this type of propelling machinery was further developed and, after the most thorough consideration, was finally adopted for the battleship New Mexico.
In the electrically-propelled battleship New Mexico, the motors were direct-connected to the propeller shafts. The stators can be connected for 24 poles or for 36 poles, giving a speed change of three to two. In wound-rotor types of motors it is necessary to change the rotor as well as the stator connections. Otherwise negative torque will be developed by certain of the rotor conductor belts. The official trials of the New Mexico showed very successful results and reports of the operation of her machinery satisfactory in every way. The steam consumption per shaft horsepower at different speeds was as follows: 21.08 knots 12.01 Ibs. of steam 19.37 knots 12.33 Ibs. of steam 14.98 knots 12.475 Ibs. of steam 10.26 knots 13.96 lbs. of steam The electrical propulsion equipment of the New Mexico was furnished by the General Electric Co.
The New Mexico was one of a group of three vessels of about 32,000 tons designed load displacement. The other two vessels of the class, the Idaho and the Mississippi, are fitted with turbine machinery. The structural arrangements adopted for the two sister vessels remain practically unaltered on the New Mexico, so that one of the particular advantages of the electric drive did not show to its fullest extent in this particular installation.
The New Mexico had her dock trials 18 and 19 July 1918, and on 15 August put to sea for her official trials. This trial was conducted under decided disadvantages. The crew was new to the ship, and the ship was only a short time out of the hands of the builders. Nevertheless, the machinery soon developed its maximum power with ease and without accident of any character to the electric part of the machinery, in spite of the fact that the crew was inexperienced and that none of them, with the exception of a few officers and men, had ever before been associated with this type of machinery. It should be noted that the penalty contract weight for the propelling machinery, including all necessary auxiliaries, was 700 tons. The actual weight as installed was only 600 tons. Moreover, the actual weight of the main propelline machinery, exclusive of auxiliaries and spares, was nearly 215 tons less than the weight of corresponding machinery of the turbine-driven sister ship Mississippi.
The New Mexico was designed for a speed of 21 knots, with 26,400 shaft horse-power. The electric motors not only met the contract requirements, but on the four-hour full speed run, permitted an average speed of 21.08 knots per hour to be maintained on a total shaft horse power of 31,200. This result was accomplished in spite of the fact that the vessel had extra fuel, stores, etc., on board, making her displacement 800 tons in excess of the designed trial load displacement. In this case, moreover, the speed was adversely affected hy the paravanes, which were not contemplated in the original design and allowance for which was not made in determining the original designed speed of 21 knots.
Many advantages were claimed for the electric type of propulsion from the point of view of economy of operation, flexibility of control and adaptability of installation. This last-named quality is of particular advantage in permitting increased protection to be given to all vital portions of the machinery spaces of battleships. In this respect, it apparently had great advantages over any other type of propelling machinery. While, as already stated, the space actually occupied by the machinery on the New Mexico is practically the same as that occupied by the turbine machinery on the sister ships Mississippi and Idaho, this fact is due rattier to a similar arrangement of machinery spaces having been adopted in the original design of all these vessels.
The good performance of the New Mexico on trial was maintained during the first 18 months of her subsequent service, and electric drive was selected for the main propelling machinery of the six battle cruisers of the U.S.S. Lexington class and the six battleships of the U.S.S. South Dakota class.
All BB-40 New Mexico Class units 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.
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