The Decision Not to Build:
By mid-1942, U.S. naval authorities concluded that aircraft carriers would contribute more to victory in the Pacific than battleships . The battleships currently under construction (six of the Iowa class, closely following the four South Dakotas) would provide an ample insurance policy against Japanese battleship construction, while also serving as an effective carrier escort force.
The USN also devoted resources to the Alaska class, a group of six “large cruisers,” “battlecruisers,” or “light battleships,” depending on your preference. While these ships could not contribute as much to the line of battle as Montana, they could conduct shore bombardment, carrier escort, and surface warfare missions much more cheaply.
The Montanas had little to contribute. Slower than the Iowas, but carrying roughly the same anti-aircraft armament, they could not perform the carrier escort mission any more effectively. They would, however, take up material and yard space dedicated to carriers and escort ships. Consequently, since the USN determined that it would struggle to find a job for the Montanas even if they entered service before the war ended, it decided to cut bait, even before the keels of the ships were laid.
However, the Montana hull design became the foundation for the Midway class aircraft carrier, the first of which entered service immediately following the end of hostilities. The ships of the Midway class would serve for most of the Cold War, with the last retiring in the 1990s.
What Might Have Been:
The Montanas would have been immensely powerful ships, probably more powerful than their Japanese (or German, or Soviet) counterparts. Battleship combat was an inherently risky endeavor . Nearly every salvo has a chance of getting a lucky hit that strikes a magazine, sending the victim to the bottom in minutes. Nevertheless, the Montanas would have been the favorites in any scrum; they could throw more weight, hit harder, and hit more accurately than any of the competitors.
The only question is who they would have fought. HIJMS Yamato sank under a barrage of bombs and torpedoes two months before the projected completion date of USS Montana. The German and Soviet ships didn’t make it much farther than the Montanas, although Stalin nursed the idea of building super-battleships into the 1950s.
Had the U.S. built the Montanas, they likely would have had similar post-war careers to those of the South Dakotas. Because of their speed, the Iowas were more useful at every job except fighting other battleships. Having built the ships in the late 1940s, the USN would have sold them for scrap in the early 1960s.
The Final Salvo:
The Montanas were designed to fight a different World War II than the one that happened. Had they begun to enter service in 1945, they would have joined an armada of twelve modern battleships, against much smaller expected Japanese construction. The howls of battleship aficionados notwithstanding, the U.S. Navy made the right choice when it cancelled the ships in favor of more useful vessels.