The South Dakota class was a group of four fast battleships built by the United States Navy. They were the second class of battleships to be named after the 40th state; the first were designed in the 1920s and canceled under the terms of the Washington Naval Treaty.Four ships comprised the class:,,, and . They were designed to the same treaty standard displacement limit of 35000LT as the preceding and had the same main battery of nine 16"/45 caliber Mark 6 guns in three-gun turrets, but were more compact and better protected. The ships can be visually distinguished from the earlier vessels by their single funnel, compared to twin funnels in the North Carolinas.
Construction began shortly before World War II, with Fiscal Year (FY) 1939 appropriations. Commissioning through the summer of 1942, the four ships served in both the Atlantic, ready to intercept possible German capital ship sorties, and the Pacific, in carrier groups and shore bombardments. All four ships were retired shortly after World War II; South Dakota and Indiana were scrapped in the 1960s, Massachusetts and Alabama were retained as museum ships.
The preceding two s had been assigned to the FY1937 building program, and in 1936, the General Board met to discuss the two battleships to be allocated to FY1938. The General Board argued for two more North Carolinas, but Admiral William H. Standley, the Chief of Naval Operations, wanted the ships to be of a new design. That meant construction could not begin by 1938, so the ships were assigned to FY1939. Design work started in March 1937 and the draft for two battleships was formally approved by the Secretary of the Navy on 23 June. More specific characteristics for the two ships were ironed out, and those were approved on 4 January 1938. The ships were formally ordered on 4 April 1938.
Due to the deteriorating international situations in Europe and Asia, Congress authorized a further two battleships of the new design, for a total of four, under the Deficiency Authorization of 25 June 1938. The "Escalator Clause" of the Second London Naval Treaty had been activated in the U.S. Navy so it could begin work on the follow-on s, but Congress was willing to approve only the 35,000-ton battleships. A number of deficiencies in the preceding North Carolinas were to be fixed in the South Dakotas; these included insufficient underwater protection and turbine engines not of the most recent technology. The North Carolinas also did not have sufficient space to act as fleet flagships, so the lead ship of the new class was designed with an extra deck on the conning tower specifically for this purpose, although the increase in space and weight from this necessitated removal of two twin 5-inch dual-purpose (DP) gun mounts.
There was a great deal of debate on the requirements for the new battleships. The design board drew up a number of proposals; one called for a ship with nine 16adj=onNaNadj=on guns in three triple turrets, 5.9adj=midNaNadj=mid deck armor that would have made the ship immune to plunging fire out to 30000yd, and a top speed of at least 23kn. The belt armor was a much more intractable problem; the 16-inch gun could penetrate 13.5inches of plate, the thickest in an American battleship at the time, even at . To proof the ship against her own armament—a characteristic known as "balanced armor"—the main belt would have to be increased to, which would have increased the weight of the vessel to prohibitive levels. To mitigate this problem, sloped armor was proposed; it was infeasible to use inclined armor in an external belt, because it would compromise stability to a dangerous degree. Instead, an internal armor belt was constructed behind unarmored hull plates. This had serious drawbacks, however; it complicated the construction process, and if the armored belt was damaged, the external plating would have to be cut away first before the belt could be repaired.
To minimize the drawbacks of the inclined belt, it sloped outward from the keel, then back in towards the armored deck. This meant that shells fired at relatively close range would hit the upper portion of the belt at an angle, which maximized armor protection. However, the effectiveness of the upper portion of the belt was degraded at longer ranges, because plunging fire would strike it at an angle closer to the perpendicular, increasing their ability to penetrate the armor. It did reduce the area that needed to be covered by the armored deck, which saved additional weight. This enabled the upper belt to be thicker, which to an extent ameliorated the vulnerability to plunging fire. Because the belt was internal, it provided the opportunity to extend it to the inner portion of the double bottom, which gave the ship better underwater protection than the North Carolinas. Ultimately, the complex double incline belt armor was abandoned when it became apparent that a single slanted belt could provide similar protection, and save several hundred tons of weight.
The size of the hull was also a problem: a longer hull generally equates to a higher top speed, but requires more armor to protect it. In order to keep a higher top speed on a shorter hull, higher-performance machinery is required. Since the South Dakota design was much shorter than the preceding North Carolinas— compared to, respectively—the new ships would need improved machinery than would otherwise have been used in shorter hulls in order to retain the same speed as the longer ships. The design initially called for a top speed of at least, which was deemed sufficient to keep up with opposing battleships and outrun surfaced submarines. However, in late 1936, cryptanalysts deciphered radio traffic from the Japanese navy which revealed that the battleship was capable of speeds in excess of 26kn.
To counter this, it was determined a top speed of 25.8kn26.2kn was possible if the power plant from North Carolina could be reduced in size enough to fit in the tighter hull of South Dakota. In order to do so the boilers were positioned directly above the turbines in the same arrangement to have been used in the 1916 s. The boilers were then rearranged several times so they were staggered with the turbines, eventually ending directly alongside the turbines. The propulsion system was arranged as close together as possible, and the evaporators and distilling equipment were placed in the machinery rooms. This provided enough additional space behind the armored belt to add a second plotting room.
By this time, the design process had established that the hull was to be 666feet between perpendiculars and incorporate the single internal sloped armor belt. However, in case of rejection by the General Board, naval architects produced a series of alternatives. Among these were longer, faster ships armed with 14-inch guns in triple turrets, slower ships with 14-inch guns in quadruple turrets, improved versions of the North Carolina class, and a ship of 27kn armed with nine 16-in guns in a similar configuration to the North Carolinas.
Arguments arose, frequently over the issue of speed; the Commander in Chief, United States Fleet (CINCUS) refused to allow the new ship to drop below, the Battle Force argued at least was necessary to maintain homogeneity in the line of battle, and the president of the War College maintained a fast ship was optimal, but the navy would continue to operate the older battleships until the 1950s and so a higher speed was not strictly necessarythough, crucially, it would mean the class would have been too slow to act in what would emerge as the most critical role for battleships, as escorts for fast carrier task forces. The primary 666-ft design was the only plan that could meet the specified requirements for speed, protection, and the nine 16-inch guns. By late 1937 a proposed design was agreed on, requiring only small modifications to save weight and increase the fields of fire. Berths for the crew, even the staterooms for senior officers, along with mess halls were reduced in size, and ventilation ports were completely removed, forcing the ship to rely completely on artificial air circulation.
Despite the compromises made, naval historians William Garzke and Robert Dulin would later argue that the South Dakota-class ships were the best treaty battleships ever built. The naval historian Norman Friedman stated that the South Dakota design was "a remarkable achievement within very constricting treaty limits." Moreover the final commitment to a higher speed presaged the development of the subsequent Iowa class—the largest, fastest, and final U.S. battleships. As Friedman has written:
The South Dakota–class battleships were 666feet long at the waterline, 680feet overall, and 108inchesft2inchesin (ftin) in beam. The design standard displacement was, approximately 1.2% overweight; when the ships were commissioned in 1942, the considerable increase in anti-air armament from the contract design increased standard displacement to (Indianas calculated value on 12 April 1942). Full load displacement was when commissioned, with a mean draft of 34feet at this displacement. At the design combat displacement of, the mean draft was 33feet while metacentric height was 7.18feet. The addition of more anti-aircraft mounts during the ships' service in World War II increased the full load displacement considerably towards the end of the war; by 1945, South Dakotas full load displacement was some, and Massachusetts reached up to at emergency load.
The hull featured a bulbous bow, triple bottom under the armored citadel, and skegs, characteristics shared by all American fast battleships. Unlike the preceding North Carolina-class and the subsequent Iowa-class, the South Dakotas mounted the outboard propulsion shafts in skegs rather than the inboard ones. Compared to the North Carolinas, the slightly shorter hull form resulted in improved maneuverability, and the vibration problems had been considerably reduced.
The South Dakota–class battleships carried a main battery of nine 16inches/45 caliber Mark 6 guns in three three-gun turrets, identical to the North Carolina-class. Two of these turrets were placed in a superfiring pair forward; the third turret was mounted aft of the main superstructure. These guns fired a 2700lb Mark 8 armor-piercing (AP) shell at a rate of two per minute per gun. The guns could either use a full propellant charge of 535lb, a reduced charge of 295lb, or a reduced flashless charge of 315lb. This provided a muzzle velocity of 2300ft/s for the AP shell with the full propellant charge, while the reduced version provided a correspondingly lower muzzle velocity of . 130 shells were stowed for each gun, which came to a total of 1,170. The guns in all three turrets could elevate to 45 degrees, but only I and III turrets could depress to −2 degrees; the superfiring II turret was not able to depress. This enabled a maximum range of 36900yd with the Mark 8 projectile. The turrets were able to train 150 degrees in both directions from the centerline, which enabled a wide arc of fire. The guns could be elevated or depressed at a rate of 12 degrees per second, and the turrets could train at 4 degrees per second.[1]