The first South Dakota class was authorized 4 March 1917, and keels were laid down in 1920 for six ships. However, as the Washington Naval Treaty prohibited their completion, construction was halted 8 February 1922, and the unfinished hulls were sold in 1923. The first South Dakota class was an outgrowth of the Standard type battleships, though a greatly modified form: Displacement would have been 12,000 tons greater than the other Standards, with only a two-knot increase in speed. The class was ordered in the same program that created the Lexington-class battlecruisers; the Lexingtons made better conversion hulls because they were further along in their construction and were designed for a far higher speed. Two Lexington hulls were converted to Lexington-class aircraft carriers, the remaining ten ships of the 1917 shipbuilding program - four battlecruisers and six battleships - were scrapped. All of the names of the ships would be reused for later World War II battleships: North Carolina was the exemplar of a two-ship class; South Dakota, Indiana and Massachusetts would be members of a new South Dakota class which bore no resemblance to this design; Iowa would be the lead ship of the last class of American battleships built; Montana would have been the exemplar of a new class, but was cancelled in favor of new aircraft carriers before being laid down.