In the early 1940s, the U.S. Navy still expected to need huge, first rate battleships to fight the best that Japan and Germany had to offer . The North Carolina, South Dakota, and Iowa class battleships all involved design compromises. The Montanas, the last battleships designed by the U.S. Navy (USN), would not.
Origins of the Design:
The interwar system of naval treaties allowed the United States to restart battleship construction in the late 1930s. The first designs (the North Carolina and South Dakota classes) complied with the restrictions of the treaties, which limited battleship size to 35,000 tons. An escalator clause kicked in after Japan failed to renew its treaty obligations, allowing the construction of the 45,000 Iowa class, which would use the extra displacement to carry slightly heavier guns, and more importantly to add five knots of speed.
The fast, slim Iowas class ships , however, diverged from the historical practice in battleship construction in the United States. Unlike their counterparts in other countries, U.S. battleship admirals preferred to sacrifice speed for firepower and protection. The USN never built any battlecruisers (although it intended to do so after World War I), and initially expected its replacement battleships to sail at 23 knots, four knots slower than any foreign contemporary. The USN bumped that to 28 when it realized foreign navies were building ships that could make closer to 30 knots. The Iowas could make 33 knots (at least on paper) because the USN wanted battleships that could escort its new fast carriers.
The Montanas didn’t drop all the way back to 23, but they did represent a step back to the precedent established by the North Carolina and South Dakota classes. They displaced 18,000 tons more than the Iowas, but spent that displacement on armor and main battery, rather than on speed. Crucially, the USN made the decision to build them too large to pass through the Panama Canal, which Japanese designers of the time had believed was a hard ceiling on the size of U.S. battleships.
The five names selected were Montana, Ohio, Maine, New Hampshire, and Louisiana. Of these, the last four recycled names from pre-dreadnought battleships, all of which had been scrapped after World War I. The first, Montana, recycled a name that was originally intended for the first South Dakota class of battleships, which were cancelled in the wake of the Washington Naval Treaty. Apart from Hawaii, Montana is the only state never to have an operational battleship named in its honor.
How They Stacked Up:
In appearance the Montanas were very similar to the Iowa class, with the biggest visible differences coming in size and main armament. The Montanas would have carried 12 16”/50 guns in four triple turrets, and would have displaced about 65,000 tons. They were to carry 16” belt armor and 9” deck armor, a substantial increase on the Iowas. However, they could only make 28 knots. The secondary armament was largely the same as the Iowas (and the preceding battleship classes), but with more deck space they could eventually have carried a heavier anti-aircraft armament.
The Montanas would have outclassed anything the British, French, or Italians had even conceived of building. The most obvious opponent for the Montanas were the Japanese Yamatos. The Montanas would have been slightly faster than the Yamatos, with a much heavier broadside. The 16”/50 weapons had greater penetrating power than the Japanese 18.1” gun, giving the U.S. ships a significant advantage. Advances in radar fire control and range finding  would also have worked to the benefit of the U.S. ships.
However, it’s worth noting that the Yamatos commissioned in 1942, before the scheduled keel laying of Montana. Even given the exceptionally fast construction schedule of U.S. warships in World War II, Montana would have entered service some three years after the Yamatos, make comparison imprecise. Moreover, the notional follow-on battleships (“Super Yamato” and “Super Duper Yamato,”  as they are colloquially known) would have substantially exceeded the Montanas in size and armament.
Apart from the Japanese, the only serious competitors in the “super-battleship” weight class were the Soviet Sovetsky Soyuz class, and the German H-39 class. Both of these types were nearly as large as the American and Japanese ships, and carried 16” guns. However, both the Soviet and German designs had major deficiencies, and in the Soviet case industrial shortcomings meant that the ships would have suffered from big operational problems. In any case, the arrival of war led to the cancellation of every super-battleship class except for the first two Yamatos.
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.
Robert Farley , a frequent contributor to TNI, is author of The Battleship Book . He serves as a senior lecturer at the Patterson School of Diplomacy and International Commerce at the University of Kentucky. His work includes military doctrine, national security, and maritime affairs. He blogs at Lawyers, Guns and Money  and Information Dissemination  and The Diplomat .