The first South Dakota class was a group of six battleships that were laid down in 1920 for the U.S. Navy, but were never completed. They would have been the largest, most heavily armed and armored battleships in the world and, designed to achieve 23 knots (43 km/h; 26 mph), represented an attempt to catch up with the increasing fleet speeds of its main rivals, the British Royal Navy and Imperial Japanese Navy.
The South Dakotas were authorized in 1917, but work was postponed so that the U.S. Navy could incorporate information gained from the Battle of Jutland, fought in mid-1916, in their 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 of 1922 both restricted the total battleship tonnage allowed the U.S. Navy, and limited individual ship size to 35,000 long tons (36,000 t), construction was halted in early 1922. The unfinished hulls were scrapped the following year, the guns were transferred to the U.S. Army and their boilers and armor were used to modernize older battleships. wiki