and BB-66) were approved for construction on 12 July 1940, with the last two intended to be the first ships of the Montana class. The Navy had been considering large battleship design schemes since 1938 to counter the threat posed by potential battleships of the Imperial Japanese Navy, which had refused to sign the Second London Naval Treaty and furthermore refused to provide details about its s. Although the Navy knew little about the Yamato class, some rumors regarding the new Japanese battleships placed their main gun battery caliber at . The potential of naval treaty violations by the new Japanese battleships resulted in the remaining treaty powers, Britain, France, and the United States, invoking the tonnage "Escalator Clause" of the Second London Naval Treaty in June 1938, which raised the maximum standard displacement limit from to . The increased displacement limit allowed the Navy to begin evaluating 45,000-ton battleship designs, including "slow" schemes that increased firepower and protection over previous designs and also "fast" schemes. The "fast" design evolved into the Iowa class while the "slow" design, with main armament battery eventually settled on twelve guns and evolution into a 60,500-ton design, was assigned the name Montana and cleared for construction by the United States Congress under the Two-Ocean Navy Act on 19 July 1940; funding for the new ships was approved in 1941. The five ships, the last battleships to be ordered by the Navy, were originally to be designated BB-65 through BB-69; however, BB-65 and BB-66 were subsequently re-ordered as Iowa-class ships, and , in the Two Ocean Navy Act due to the urgent need for more warships, and the Montanas were redesignated BB-67 through BB-71. Completion of the Montana class, and the last two Iowa-class battleships, was intended to give the US Navy a considerable advantage over any other nation, or probable combination of nations, with a total of 17 new battleships by the late 1940s. The Montanas also would have been the only American ships to rival Japan's massive and her sister in size and raw firepower. Design Preliminary planning for the Montana-class battleships took place in 1939, when the aircraft carrier was still considered strategically less important than the battleship. The initial schemes for what would eventually become the Montana class were continuations of various 1938 design studies for a 45,000-ton "slow" battleship alternative to the "fast" battleship design that would become the Iowa