class. The "slow" battleship design proposals had a maximum speed of and considered various main gun battery options, including /45 cal, 16-inch/50 cal, 16-inch/56 cal, and /48 cal guns; a main battery of twelve 16-inch/50 cal guns was eventually selected by the General Board for offering the best combination of performance and weight. The initial design schemes for the Montana class were given the "BB65" prefix. In July 1939, a series of 45,000-ton BB-65 design schemes were evaluated, but in February 1940, as a result of the outbreak of World War II and the abandonment of the naval treaties, the Battleship Design Advisory Board moved to larger designs capable of simultaneously offering increased armament and protection. The design board issued a basic outline for the Montana class that called for it to be free of beam restrictions imposed by the extant Panama Canal, be 25% stronger offensively and defensively than any other battleship completed or under construction, and be capable of withstanding the new "super heavy" armor-piercing (AP) shells used by US battleships equipped with either the 16-inch/45 cal guns or 16-inch/50 cal Mark 7 guns. No longer restricted by treaty displacement limits, naval architects were able to increase armor protection for the new BB65 design schemes, enabling the ships to withstand enemy fire equivalent to their own guns' ammunition. In conjunction with the Montana class, the Navy also planned to add a third set of locks to the Panama Canal that would be wide to enable ship designs with greater beams; these locks would have been armored and would normally be reserved for use by Navy warships. Although freed of the beam restriction from the extant Panama Canal, the length and height of the BB65 designs had to take into account one of the shipyards at which they were to be built: the New York Navy Yard slipways could not handle the construction of a ship more than , and vessels built there had to be low enough to clear the Brooklyn Bridge at low tide. Consequently, the yard's number 4 dry dock had to be enlarged and the ships would be floated out rather than conventionally launched. The larger BB-65 design studies would again settle on a main armament of twelve 16-inch/50 cal guns while providing protection against the "super heavy" AP shells. After debate at the design board about whether the Montana class should be fast, achieving