The First South Dakota Class

The Washington Naval Treaty of 1922 brought about major changes in the design of the battleship, most notably cancelling most of the ships being built in American and Japanese yards. In the United States, three classes were affected. I've previously discussed the Colorado and Lexington classes, but a third class, the South Dakotas, were cancelled entirely.

The South Dakota class as designed

The South Dakotas were ordered under the massive Naval Act of 1916, a result of Woodrow Wilson's swing towards naval expansion as the World War dragged on. Americans feared that a victorious power would turn its eyes across the Atlantic, seeking economic dominion over the United States. A fleet "second to none" would be vital to safeguarding US interests from a power with millions of battle-hardened veterans and a war indemnity from the loser. It was not apparent at the time the economic toll that the war would take on the participants, rendering any such dreams moot by 1918. The bill, on the floor of Congress when news arrived of Jutland, authorized ten battleships and six battlecruisers. While the first four were to be derivatives of the existing Tennessee class, which ultimately became the Colorados, the last six could be significantly larger, the ships the USN had been asking for since 1914.

The preliminary design of the South Daktoa

Developments in battleships in Japan and Britain, particularly reports of the British 18" gun project, meant that the General Board, responsible for US ship characteristics, wanted a bigger and more powerful vessel. There was also an upward trend in battleship speed, so the initial characteristics were for a ship with 12 16" guns and a speed of 23 kts. Initial sketches with 6 twin turrets were soon discarded after successful firing trials with the triple turrets on the early Standards, and a new 16"/50 gun was developed to replace the 16"/45 used on the Colorados.¹

A few sketches were done with improved armor, but the resulting increase in the size of the ship meant that they were also discarded, except for an extra .5" on the armored deck. Secondary armament layout was a more difficult issue, due to the great length of the machinery spaces. One alternative was a twin 5" mount in a blast-proof gunhouse, although this was not adopted for unclear reasons. Another was to concentrate the guns high in the ship for best effectiveness, instead of having them low down as in previous designs. The downside was that blast high in the ship might affect the conning tower. The designers came up with an ingenious solution. The barbette of Turret 2 was made wider, and the ship and fire control spaces were built around the turret structure. This solution, while very clever, was not popular with line officers, who quite reasonably pointed out that a low ship control position was less than ideal, and that a 16" turret going off overhead was likely to be a distraction from commanding the ship. Eventually, the problem was solved by trunking together the various uptakes from the boilers into a single funnel amidships, freeing enough space for the secondary guns.

The sketch design with the conning tower integrated into Number 2 barbette

The first three ships built to this design were to have been laid down in late 1917. However, a few months after its entry into the war, the US suspended battleship construction to focus instead on vessels relevant to winning the tonnage war with the U-boats: destroyers, merchant ships, and the like. This resulted in more tweaks to the design, most notably replacing the 5"/51 guns with 6"/53s and making the turret tops thicker. More elaborate plans, most notably involving the use of sloped armor belts, were considered and discarded. The final result was a ship of 43,200 tons, a full 10,000 tons more than the Colorados, 684' long and very powerful, if a bit slow. Six ships were finally laid down in 1920 and 1921, suspended in February 1922, when the Washington Naval Treaty was being negotiated, and scrapped six months later. Five of the six names were reused for fast battleships during WWII, including the greatest vessel ever built. The sixth, Montana, was to be the lead ship of the follow-on class to the Iowas, but they also fell victim to cuts.

USS Iowa (BB-53) under construction

The South Dakotas were the last in a very successful line of American battleships. New designs for the next class of battleship were in work when the Treaty came into force, mostly focused on improved protection. This would have required several thousand more tons of displacement, and the existing design was already pushing the limits of American docking facilities. As it was, it would be a decade and a half before another American battleship was laid down.