The Montana-class battleships are one of the most fascinating “what ifs” in US naval history—a peek into an era when battleship design set engineering to the test, only to be surpassed by the sudden advent of air power and aircraft carriers. Designed in World War II as replacements for the Iowa-class, the Montanas were designed to be the largest, most technologically advanced battleships in the history of the U.S. Navy. Their history is one of grand vision, innovative design, and ultimate obsolescence.
While the Iowa-class emphasized speed to match the advance of fast carrier groups, the Montana-class reverted to a philosophy of heavy armor and toughness. Unencumbered by the limitations of treaties and earlier tonnage restrictions, designers were able to take a page from past battle experience.
The resulting ship would have displaced over 70,000 tons when loaded, with a speed of approximately 28 knots—slightly lower than the Iowas, but much more resilient in protection and firepower.
Armor was the Montana-class’s crowning achievement. Designers reverted to an external vertical belt following the internal belts of the South Dakota and Iowa classes, which were tricky to defend and maintain during combat.
The principal belt was 16.1 inches in thickness, backed by a special treatment steel plate and sloped at 19 degrees to maximize its effective thickness. At close range, this equated to about 18 inches of armor, and it was even more effective at longer ranges as shell trajectories steepened.
To counter the threat from plunging shells—armor-piercing rounds that would strike the water short of the hull—the Montanas had a lower belt in addition to the main one. 8.5 inches above magazines and 7.2 inches above machinery spaces, the secondary layer reached down to the triple bottom of the ship.
In dividing the upper and lower belts, designers achieved a balance providing protection from both heavy shells and underwater explosions, a lesson learned in years of interwar experimentation.
Horizontal protection was also impressive. Three armored layers of the deck created a strong cover for vulnerable spaces: a 2.25-inch weather deck meant to detonate approaching fuzes, a 7.05-inch armored main deck to cover the citadel, and a splinter deck between an inch thick to trap fragments. In total, this design provided almost 10 inches of horizontal protection, a big increase from earlier U.S. battleships and a formidable barrier for enemy shells or bombs dropped from aircraft.
The barbettes and primary gun turrets were also well protected. Each turret had 22.5-inch faceplates—three inches thicker than those on the Iowa-class—plus strengthened roofs and sides. Barbettes, the mounts for the turrets, were 18 to 21.3 inches thick, providing the main armament of the ship with unparalleled protection.
Such fortification would allow the Montana-class to, in theory, keep on firing even when being heavily bombarded by the enemy, maintaining its combat power during the kind of slugfest battleships were designed for.
Underwater protection was also given close consideration. The Montana-class made use of a torpedo defense system consisting of four layers of voids between the inner bulkhead and the outer hull. The two outer layers were filled with liquid to soak up explosive energy, while the inner two were empty to absorb whatever force remained. Due to the size of the ship, which was vast, this system could be constructed deeper and more efficiently than in earlier battleships, providing a substantial advantage against torpedoes.