The Montana-class battleships represented the last major concept that characterized the era when triumph at sea was gauged by the amount of heavy armor and the loudness of big naval guns. The United States intended these vessels to be the final evolution of the battleship series, and their specifications were designed to go even beyond the mighty Iowa class, both in terms of safety and lethality. However, their designs remained only as designs that never actually materialized, being overtaken by a different conception of conflict.
A Break from the Shackles of Treaty Constraints
International naval treaties during most of the early 20th century controlled what battleships could and could not be—how much displacement, gun caliber, and armor they could have. The Montana class broke those restraints overboard. At 121 feet in beam, they were so broad they could not fit through the original Panama Canal locks, leading to plans for a new, wider set of locks to service them.
Planning commenced even prior to the entry of America into World War II, with Congress approving the first two ships in 1939. The design of Montana adopted the Navy’s traditional philosophy—maximum protection and maximum firepower—even if it cost it the speed characteristic of the Iowa class.
Armor: The Heaviest Ever on a U.S. Battleship
If they were constructed, the Montanas would have been the most armoured ships ever in the history of the U.S. Navy. Their armour was designed to brush aside the enormous 2,700-pound Mark 8 “superheavy” shells—ordnance more formidable than anything the Iowa or South Dakota class had been designed to meet.
They featured their principal armor belt, a whopping 16.1 inches in thickness, externally mounted and inclined at 19 degrees for added effective resistance. Below that, another armored belt protected against “diving shells”—armor-piercing shells with the ability to go underwater and hit beneath the waterline.
Above, the layered deck armor gave excellent protection against aerial attack. A 2.25-inch weather deck, a 7.05-inch main armor deck, and a splinter deck up to 1 inch thick together protected against plunging fire and armor-piercing bombs.
The turrets were just as effective—faces as much as 22.5 inches thick, three inches greater than the Iowas, with barbettes from 18 to 21.3 inches thick. No other American battleship design was comparable in terms of turret protection.
Built to Survive Underwater Assaults
Below the waterline, the Montana class had a four-layered torpedo defense system, with liquid-filled and air-filled compartments alternating in order to absorb and distribute explosive force from torpedoes or mines. The depth of this system was among the most well-thought-out for any battleship of the period—another testament to the philosophy of the class: to endure punishment and fight on.
The Montana class would have been a steel and firepower behemoth. But before war production priorities began turning towards aircraft carriers and fast battleships, their day had passed, leaving them as legends that never sailed.
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