Model of the South Dakota-class battleship
|Name:||South Dakota class|
|Operators:||United States Navy|
|Preceded by:||Colorado class|
|Succeeded by:||North Carolina class|
|Cost:||$21,000,000 (cost limit)|
|General characteristics |
684 ft (208 m) overall660 ft (200 m) waterline
|Beam:||106 ft (32 m)|
|Draft:||33 ft (10 m) (design)|
|Speed:||23 knots (43 km/h)|
|Range:||8,000 nautical miles (15,000 km; 9,200 mi) at 10 knots (19 km/h; 12 mph)|
|Complement:||137 officers, 1404 enlisted, 75 marines|
The first South Dakota class was a class of six American battleships that were laid down in 1920 but never completed. They would have been the last dreadnoughts in the Naval Act of 1916 to be commissioned had the Washington Naval Treaty not caused their cancellation one-third of the way through their construction. They would have been the largest, most heavily armed and armored battleships in the U.S. Navy and, designed to achieve 23 knots (43 km/h), represented an attempt to abandon its 21-knot (39 km/h) standardized fleet speed and catch up with the increasing fleet speeds of its main rivals, the British Royal Navy and Imperial Japanese Navy. In this, size and secondary armament, they represented a break from the Standard-type battleship that had dominated American capital ship design for the prior five ship classes, while their use of standardized bridges, lattice masts and other features was a continuation of this practice and the increase in the number of main guns from the preceding Colorado class had long been standard U.S. naval policy. The main restriction to which they had to adhere was the ability to pass through the Panama Canal.
The South Dakotas were authorized 4 March 1917, but work was postponed so that the U.S. Navy could incorporate information gained from the Battle of Jutland, fought in 1916, in this class's final design. Work was further postponed to give destroyers and other small fighting vessels priority as they were needed urgently to fight German U-boats in the North Atlantic. Construction started only in 1920. As the Washington Naval Treaty both restricted the total allowable battleship tonnage allowed the U.S. Navy, and limited individual ship size to 35,000 tons, construction was halted 8 February 1922. While the unfinished hulls (most over 30% completed) were scrapped in 1923, the armor plates already prepared were left unused in the shipyards until World War II. The 40- and 50-ton plates intended for Montana, for instance, were sent in 1941 or 42 to the Panama Canal to reinforce the defenses and locks there. The 16" guns were transferred to the U.S. Army for use in coastal artillery.
The design characteristics of the South Dakotas closely followed those of the Tennessee and Colorado classes. The increase in the number of main guns was a continuation of U.S. Navy practice from the beginning of the dreadnought era. Like the Tennessees and Colorados, they would have been fitted with standard bridges and lattice masts. Although Norman Friedman describes the South Dakotas as the ultimate development of the series of U.S. battleships that began with the Nevada class, they were also a departure in size, speed and intermediate armament from the "Standard Type" that characterized the Nevada through Colorado classes. The main restriction imposed on them by the Navy was the ability to pass through the Panama Canal. This was a policy to which capital ship designs were to strictly adhere due to the savings in time when ships needed to travel from the Pacific Ocean to the Atlantic or vice versa.
The South Dakotas would have been 684 feet (208 m) long, 106 feet (32 m) wide and displaced 43,200 tons.
Turbo-electric propulsion, which the U.S. Navy had adopted for capital ships with the New Mexico-class battleship, was continued in this class. This circumvented one potential bottleneck since American companies struggled to produce the very large reduction gears necessary for such big ships. The separate turbine normally needed to steam astern could be eliminated since the direction of rotation could simply be reversed by means of the commutators on the electric motors, which ensured rapid changeover. This also allowed the ships to apply full engine power in reverse, which was impossible with traditional turbines (the reverse turbine was rarely as large as the main turbines). The turbines could run at their optimum speed, without regard to propeller speed, which was economical on fuel. The machinery could also be subdivided more tightly, which could increase the ships' ability to withstand torpedo hits. On the down side, the machinery was heavier and bulkier than geared turbines and there was the danger of high voltage to the crew. Also, despite elaborate attempts at insulation, protection against moisture damage or flooding (from battle damage and other causes) remained inadequate.
In the South Dakotas, two turbo generators (General Electric for Indiana and Montana, Westinghouse for the others) would have been coupled to two AC alternators of 28,000 KVA and 5000 volts. These would feed four electric motors, one per propeller shaft, each rated at 11,200 kilowatts (15,000 hp) of direct current (DC). Sixteen water-tube boilers, each in their own individual compartment, would have lined the turbine rooms to provide steam for the generators. With a total of 60000 electrical horsepower (EHP), top speed was expected to be 23 knots (43 km/h).
The South Dakotas were slated to carry twelve 16"/50 caliber Mark 2 gun in four triple turrets. These fired the same 2,100-pound (950 kg) shell as the Mark 1 of the Colorado class with a muzzle velocity of 2,650 feet per second (810 m/s) to an effective range of 44,600 yards (40,800 m). at a maximum elevation of 46 degrees. The Mark 2 was not fitted on any ship; the 16"/50s used later on the Iowa-class battleships were of a lighter Mark 7 design. With the cancellation of the South Dakotas and Lexingtons, the existing guns were transferred to the army and installed in coastal defense batteries in place of the more massive and much more expensive 16"/50 caliber M1919 gun.
Secondary armament would have been sixteen 6"/53 caliber guns. Twelve of these were to be on Mark 13 mountings in unarmored casemates; the rest would have been placed open on the superstructure deck. This was a departure from the 5"/51 caliber guns used in U.S. battleships since the Florida class of 1908. The 6"/53 fired a 105-pound (48 kg) projectile at a velocity of 3,000 feet per second (910 m/s) to a maximum range of 21,000 yd (19,000 m) at a maximum elevation of 20 degrees. They were installed in Omaha-class cruisers when the South Dakotas were canceled under the Washington Naval Treaty and several large submarines built during the 1920s. Later light cruisers would use the similar but more potent 6"/47 caliber gun. 
According to Siegfreid Breyer, the protective system of the South Dakotas was designed to be 50 percent stronger than that of HMS Hood. Belt armor was a consistent 13.5 inches (340 mm), not tapered. The upper armored deck, 2.5–3.5 inches (64–89 mm) thick, rested on the top edge of the belt armor. One deck below this was a second armored belt, 1.5–2.5 inches (38–64 mm). Fore and aft transverse armored bulkheads of 13.5 inches (340 mm) sealed off the machinery and magazines. Past these, the lower armored deck continued at a thickness of 6 inches (150 mm) to the ends of the ship. Forward, above this, the upper armored deck continued at a thickness of 3.5 inches (89 mm). Flue gas exits were armored for one deck upwards from the upper armored deck at a thickness of 13.5 inches (340 mm)
Protection for the main guns was also considerable. Barbettes were 13.5 inches (340 mm) above the upper armored deck and 5.5 inches (140 mm) from there to the lower armored deck. Turret rings were also armored to a thickness of 13.5 inches (340 mm). Turret faces were 18 in (457 mm), sides 9–10 inches (230–250 mm), top 5 inches (130 mm) and rear 9 inches (230 mm). Conning tower armor was 16 in (406 mm) on the front and sides, 8 inches (200 mm) on top. Underwater protection was more subdivided longitudinally than in the Colorados but was otherwise similar, with three armored bulkheads .75 inches (19 mm) thick from the lower armored deck to the ship's bottom to the armored transverse bulkheads near the ends.
|Name||Hull No.||Shipyard||Laid down||Suspended||Canceled||% Completed||Struck|
|South Dakota||BB-49||New York Naval Shipyard||15 March 1920||8 February 1922||17 August 1922||38.5%||10 November 1923|
|Sold for scrap 25 October 1923 to Steel Scrap Co., Philadelphia, Penn. Scrapping completed 15 November 1924.|
|Indiana||BB-50||New York Naval Shipyard||1 November 1920||8 February 1922||17 August 1922||34.7%||25 October 1923|
|Scrapped on slip.|
|Montana||BB-51||Mare Island Naval Shipyard||1 September 1920||8 February 1922||17 August 1922||27.6%||24 August 1923|
|Sold for scrap 25 October 1923 to Learner and Rosenthal, Oakland, Cali.|
|North Carolina||BB-52||Norfolk Naval Shipyard||12 January 1920||8 February 1922||17 August 1922||36.7%||10 November 1923|
|Sold for scrap 25 October 1923.|
|Iowa||BB-53||Newport News Shipbuilding||17 May 1920||8 February 1922||17 August 1923||31.8%|
|Sold for scrap 8 November 1923.|
|Massachusetts||BB-54||Fore River Shipyard||4 April 1921||8 February 1922||17 August 1923||11.0%||10 November 1923|
|Sold for scrap 8 November 1923 to the Steel Scrap Co., Philadelphia, Penn.|
The names of five of the planned South Dakota-class were eventually re-used for a number of the US Navy's fast battleships constructed during the late 1930s and commissioned after the US entry into World War II:
|Wikimedia Commons has media related to South Dakota class battleships (1920).|