South Dakota-class battleship (1920)

The first South Dakota class was a class of six battleships, laid down in 1920 but never completed. They would have been the last dreadnoughts in the United States's 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, represented an attempt to abandon its 21 knot 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 last few 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 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 restricted both the total allowable battleship tonnage allowed the U.S. Navy, and limited individual ship size to 35000 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 coast artillery.

Design
The design characteristics of the South Dakotas closely followed those of the and  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, they were also a departure in size, speed and intermediate armament from the "Standard Type" that characterized the Nevada through 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.

Overall dimensions
The South Dakotas would have been 684 ft long, 106 ft wide and displaced 43,200 tons.

Propulsion
Turbo-electric propulsion, which the U.S. Navy had adopted for capital ships with the, 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 11200 kW 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.



Main guns
The South Dakotas were slated to carry carried twelve 16-inch 50 caliber Mark 2 guns in four triple turrets. These fired the same 2100 lb shell as the Mark 1 of the Colorado class with a muzzle velocity of 2650 ft/s to an effective range of 44600 yd. at a maximum elevation of 46 degrees. The Mark 2 was not fitted on any ship; the 16"/50s used later on the s 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 Army's more massive and much more expensive M1919 16-inch Coast Gun.

Secondary guns
Secondary armament would have been sixteen 6 in 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 in 51 caliber guns used in U.S. battleships since the of 1908. The 6"/53 fired a 105-pound (47.6 kg) projectile a velocity of 3,000 feet per second (900 m/s) to a maximum range of 21000 yd at a maximum elevation of 20 degrees. They were installed in s when the South Dakotas were canceled under the Washington Naval Treaty and would become a mainstay of U.S. Navy light cruisers and submarine cruisers built during the 1920s.

Armor
According to Siegfreid Breyer, the protective system of the South Dakotas was designed to be 50 percent stronger than that of HMS Hood (51). Belt armor was a consistent 13.5 in, not tapered. The upper armored deck, 2.5 - 3.5 in thick, rested on the top edge of the belt armor. One deck below this was a second armored belt, 1.5 - 2.5 in. Fore and aft transverse armored bulkheads of 13.5 in sealed off the machinery and magazines. Past these, the lower armored deck continued at a thickness of 6 in to the ends of the ship. Forward, above this, the upper armored deck continued at a thickness of 3.5 in. Flue gas exits were armored for one deck upwards from the upper armored deck at a thickness of 13.5 in

Protection for the main guns was also considerable. Barbettes were 13.5 in above the upper armored deck and 5.5 in from there to the lower armored deck. Turret rings were also armored to a thickness of 13.5 in. Turret faces were 18 in, sides 9 - 10 in, top 5 in and rear 9 in. Conning tower armor was 16 in on the front and sides, 8 in on top. Underwater protection was more subdivided longitudinally than in the Colorados but was otherwise similar, with three armored bulkheads .75 in thick from the lower armored deck to the ship's bottom to the armored transverse bulkheads near the ends.

Ships in class
Ship Name:BB-49 South Dakota Laid Down:15 March 1920 Launched: N/A Commissioned: N/A Built By: New York Naval Shipyard Decommissioned/Fate: Cancelled 8 February 1922 @ 38.5% complete. Sold for scrap 25 October 1923. Struck 10 November 1923.

Ship Name: BB-50 Indiana Laid Down:1 November 1920 Launched: N/A Commissioned: N/A Built By: New York Naval Shipyard Decommissioned/Fate: Cancelled 8 February 1922 @ 34.7% complete. Struck 25 October 1923, scraped on slip.

Ship Name:BB-51 Montana Laid Down:1 September 1920 Launched: N/A Commissioned: N/A Built By: Mare Island Navy Yard Decommissioned/Fate: Cancelled 8 February 1922 @ 27.6% complete. Struck 17 August 1922. Sold for scrap 25 October 1923.

Ship Name:BB-52 North Carolina Laid Down:12 January 1920 Launched: N/A Commissioned: N/A Built By: Norfolk York Naval Shipyard Decommissioned/Fate: Cancelled 8 February 1922 @ 36.7% complete. Sold for scrap 25 October 1923. Struck 10 November 1923.

Ship Name: BB-53 Iowa Laid Down: 17 May 1920 Launched: N/A Commissioned: N/A Built By: Newport News Shipbuilding Corporation Decommissioned/Fate: Suspended 8 February 1922 @ 31.8% complete. Cancelled 17 August 1923. Sold for scrap 8 November 1923.

Ship Name: BB-54 Massachusetts Laid Down: 4 April 1921 Launched: N/A Commissioned: N/A Built By: Fore River Shipbuilding Company Decommissioned/Fate: Suspended 8 February 1922 @ 11.0% complete. Cancelled 17 August 1923. Sold for scrap 8 November 1923. Struck 10 November 1923.

Class Notes: Construction was suspended on all ships Feb. 8, 1922 and cancelled on Nov. 8-10, 1923 due to the limitations on naval construction of the Washington Naval Treaty.