Second London Naval Treaty
Due to the deteriorating international situations in Europe and Asia, Congress authorized a further two battleships of the new design, for a total of four, under the Deficiency Authorization of 25 June 1938. The "Escalator Clause" of the Second London Naval Treaty had been activated in the U.S. Navy so it could begin work on the follow-on s, but Congress was willing to approve only the 35,000-ton battleships. A number of deficiencies in the preceding "North Carolina"s were to be fixed in the "South Dakota"s; these included insufficient underwater protection and turbine engines not of the most recent technology.