The Montana-class battleships were planned as successors of the for the United States Navy, to be slower but larger, better armored, and with superior firepower. Five were approved for construction during World War II, but changes in wartime building priorities resulted in their cancellation in favor of continuing production of s and Iowa-class battleships before any Montana-class keels were laid. Their intended armament would have been twelve Mark 7 guns in four 3-gun turrets, up from the nine Mark 7 guns in three turrets used by the Iowa class. Unlike the three preceding classes of battleships, the Montana class was designed without any restrictions from treaty limitations. With an increased anti-aircraft capability and substantially thicker armor in all areas, the Montanas would have been the largest, best-protected, and most heavily armed US battleships ever. They also would have been the only class to rival the Empire of Japan's s in terms of displacement. Preliminary design work for the Montana class began before the US entry into World War II. The first two vessels were approved by Congress in 1939 following the passage of the Second Vinson Act. The Japanese attack on Pearl Harbor delayed the construction of the Montana class. The success of carrier combat at the Battle of the Coral Sea and, to a greater extent, the Battle of Midway, diminished the perceived value of the battleship. Consequently, the US Navy chose to cancel the Montana class in favor of more urgently needed aircraft carriers as well as amphibious and anti-submarine vessels. Because the Iowas were far enough along in construction and urgently needed to operate alongside the new Essex-class aircraft carriers, their orders were retained, making them the last US Navy battleships to be commissioned. History As the political situation in Europe and Asia deteriorated in the prelude to World War II, Carl Vinson, the chairman of the House Committee on Naval Affairs, instituted the Vinson Naval Plan. It aimed to get the Navy into fighting shape after the cutbacks imposed by the Great Depression and the two London Naval Treaties of the 1930s. As part of the overall plan, Congress passed the Second Vinson Act in 1938, which was promptly signed by President Franklin D. Roosevelt and cleared the way for construction of the four fast battleships and the first two fast battleships (hull numbers BB-61 and BB-62). Four additional battleships (with hull numbers BB-63, BB-64, BB-65,