Montana Class vs. Iowa Class : Reversion back to Traditional Battleship Design

montana class vs. iowa class

The Iowa class battleship was a radical departure from traditional US battleship design practice. The US had long advocated for firepower and armor at the expense of speed. While the Iowa class was the first true fast battleship and arguably a massive success, Naval designers were quick to begin work on a successor design. A battleship that once again opted for maximum firepower and armor, the Montana class battleships. In this article, we will examine the Montana class vs. Iowa class , investigating the evolution of battleship design that led to America’s never built super battleship. We will also see how the two ships compared with one another and attempt to debunk a few myths that have built up around these ships.

montana class vs. iowa class

The Concept

In 1938 the Navy had already given the go ahead for the construction of four South Dakota class battleships and the first two of the latest Iowa class battleships. However at the exact same time, the Navy was concerned about potential weaknesses in their battleship line. The Navy’s latest and most powerful battleships, the Iowa class, were originally designed for operations outside of the main battleship line. The South Dakota and North Carolina class battleships were powerful vessels, but the Navy was mindful of larger battleships that might be in Japanese service. The Navy had long suspected that Japan had adhered rather loosely to the naval treaties. Japan had made it a point to debut the largest guns. They were the first nation to use 14″ and then 16″ weapons. Many suspected that Japan might potentially build battleships more powerful than those in the US.iowa class vs. montana class


The initial plan called for battleships of 45,000 tons. Slower than the Iowa class, these ships would sacrifice speed for more armor. However, by 1939 the Navy had heard rumors of large Japanese battleships. While 18″ guns were rumored, the Navy was in disbelief that Japan could or would manufacture such large weapons. Still, the advisory board recommended the new ships be enlarged to a displacement of 58,000 tons. The design board finally issued the following primary requirements for the new class:

  • 25% more Firepower than any battleship currently in construction.
  • 25% more protection than any battleship currently in construction.
  • The ability to withstand the new 2700lb “super heavy” projectiles fired from the 16″/50 Mark 7 gun.
  • To be free of beam restrictions imposed by the Panama Canal. (The Navy had called for the installation of new 140′ locks at this time. The Montana could have used these larger locks.)

Following these criteria, battleship designers began to debate the ship’s final characteristics.


The biggest hurdle in the design of the Montana class was the subject of speed. The United States had long advocated for armor and firepower over speed. The Iowa class was a departure from that style of thinking. Following its conception, designers had become smitten with the Idea of high speed. At first, it was debated whether or not the Montana class should also match the 33 knot speed of the Iowa class. To achieve this speed, armor would have to be reduced. However, the threat of powerful Japanese battleships convinced designers that they should revert back to armor and firepower at the expense of speed. A speed of 28 knots was chosen. Not only would this allow enough armor to resist its own firepower, a “balanced design”, but it would also allow the Montana class to operate with the North Carolina and South Dakota classes, forming a 28 knot battle line.

Iowa Class vs. Montana Class : Speed

  • Iowa Class: 212,000shp – 33knts
  • Montana Class: 172,000shp – 28knts

Compared to the Iowa class, the Montana class would have been much slower. However, the Montana class was still faster than the WW1 era battleships and matched the modern prewar battleships of the North Carolina and South Dakota classes. It was hoped that it could operate in a 28kn battle line made up of the newer battleships. The Iowa class meanwhile, was never intended to operate in the battle line, it was originally meant to operate as a backup unit, hunting down fast Japanese battleships. The speed difference between the two is only due to the nature of their intended roles.


Firepower was perhaps the easiest design aspect of the Montana class. Designers wanted at least 25% more firepower over the current battleships armed with nine 16″ guns. However, the Montana class was designed almost from the start with twelve main guns arranged in four triple turrets. While there were some calls for larger 18″ weapons, testing with the 18″/48 Mark I had revealed that slight performance gains did not make up for the vastly heavier weight. It was felt that the 16″ gun was the largest practical size and when armed with the 2700lb “super heavy” shells had more than enough penetration to deal with any potential adversary.

While the primary armament was simple, selecting the secondary armament was more difficult. While the dual-purpose 5″/38 was a very capable weapon, some designers wanted more range and power. Several designs were looked at including larger dual-purpose 6″ guns. Eventually however, the designers settled on an interim solution in the 5″/54 dual-purpose gun. Relatively compact like the 5″/38, it had a heavier projectile and higher muzzle velocity. This would allow it to engage aircraft further away while also being more effective against surface ships.

Iowa Class vs. Montana Class : Firepower

montana class vs. iowa class
The 16″/50 Mark 7 naval gun in action onboard an Iowa class battleship. This was arguably the best battleship gun ever put into service. It would have also been used on the Montana class.
  • Iowa Class:
    • 9x 16″/50 Mark 7 guns
      • Range – 42,345 yards
      • Rate of Fire – 2rpm
      • Broadside Weight – 24,300lbs
    • 20x 5″/38 DP guns
      • Range – 17,392 yards
      • AA Ceiling – 37,200′
      • Rate of Fire – 22rpm (Maximum) 18-15rpm (Sustained)
      • Broadside Weight -551lbs
  • Montana Class:
    • 12x 16″/50 Mark 7 guns
      • Range – 42,345 yards
      • Rate of Fire – 2rpm
      • Broadside Weight – 32,400lbs
    • 20x 5″/54 DP guns
      • Range – 25,909 yards
      • AA Ceiling – 51,600′
      • Rate of Fire – 18-15rpm
      • Broadside Weight – 693lbs

With the Montana class, the United States got their 25% increase in firepower and then some. In main battery firepower, the Montana enjoyed 33% greater firepower compared to the Iowa class. When firing the “super heavy” 2700lb Mark 8, the Montana class achieved a broadside weight of 32,400lbs. This would have been the heaviest broadside of any battleship ever built, surpassing even the 18.1″ guns of the Yamato (28,971lbs).

Secondary weapons would have also been improved compared to the Iowa class. The heavier weight of the 5″/54 round would have allowed for a broadside weight of 693lbs compared to the 551lbs of the Iowa class, a 25% increase. The secondary guns of the Montana class would have also have enjoyed greater range, though the heavier round would likely result in a slightly slower rate of fire.

As the Montana class was never built, its final anti-air configuration will never be known. However, it is safe to assume that it would have been at least equal to the Iowa class.


Its a common misconception that the Iowa was weakly armored. While it was incapable of resisting the firepower of its own weapons, this is only because of the introduction of the “super heavy” Mark 8. This shell drastically improved the penetration power of the 16″/50, putting it almost on par with the larger 18.1″ guns of the Yamato at range. The primary reason why the Iowa class was not armored enough to resist the Mark 8 is due to its introduction after the Iowa design was finalized. The Iowa’s armor was not weak, it was simply matched against an absurdly powerful naval shell.

Almost from the beginning, the Montana was intended to resist the mighty Mark 8 shell. Unlike the Iowa and South Dakota classes, which used an internal armored belt (a weight savings measure), the Montana returned to an external belt. 16.1″ of armor plate was mounted overĀ  1″ STS (specially treated steel). The belt was also inclined at 19 degrees, improving performance against incoming shells. Deck armor was also strengthened, with 3 individual layers producing a combined thickness of just over 9.25″ (compared to the 7.5″ deck armor of the Iowa class). The improved belt and deck armoring of the Montana class allowed it have an immunity zone from the Mark 8″ from 18,000 to 31,000 yards.

Underwater protection was also improved with the Montana class. The Iowa class had used a continuous armor belt that tapered down all the way to the keel. This was intended to prevent diving shells from damaging the ship. However, testing had shown that this negatively affected performance against torpedoes. The Montana design disconnected the main belt from the secondary belt intended to protect against diving shells. This improved the elasticity of the bulkheads, better allowing them to withstand underwater explosions. Most importantly, the greater beam of the Montana class gave its torpedo defense system greater depth compared to the Iowa.

The armor schemes of the Montana and Iowa class battleships. Note the internal armor belt of the Iowa class vs. the external armored belt of the Montana class.

Iowa Class vs. Montana Class : Armor

  • Iowa Class
    • Belt – 12.1″
    • Deck – 7.5″
    • Turrets – 19.7″ (Maximum)
    • Barbettes – 17.3″-11.6″
    • Bulkheads – 14.5″-11.3″
    • Conning Tower – 17.3″
  • Montana Class
    • Belt – 16.1″
    • Deck – 9.25″
    • Turrets – 22.5″ (Maximum)
    • Barbettes – 21.3″-18″
    • Bulkheads – 18″-15.25″

Compared to the Iowa class, the Montana enjoys greater armor. The external belt would keep more damage outside of the hull compared to the Iowa’s design. The amount of armor carried by the Montana would have made it well protected against the weaponry used by any other nation, even capable of withstanding the 18.1″ shells of the Yamato class at certain ranges. The Montana class was designed to operate on the main battle line, directly engaging the enemy battleships and expecting to survive. The Iowa, while well protected against most battleships, was designed to hunt down enemy fast battleships. Had the aircraft carrier not taken over naval combat, both the Montana and Iowa would have excelled in their respective roles.

The biggest advantage the Montana would have over the Iowa is in underwater protection. A stronger torpedo defense system and greater beam drastically improves the ability of the Montana class to resist underwater explosions. The fine hull form of the Iowa class, while aiding speed, was detrimental to underwater protection. In this category, the Montana enjoys a clear advantage of the Iowa class.

Iowa Class vs. Montana Class : Final Thoughts

Other than speed, the Montana class battleships were improvements over their predecessors in almost everyway. However, it is important to remember that the Montana class was not built to rectify weaknesses in the Iowa class. Though both were battleships, it must be remembered that each design was intended for very different purposes. The Montana was a return to traditional battleship design, a heavily armed and armored warship designed to operate in the main line of battle. The Iowa class was to operate behind the main line, intercepting any ship fast enough to avoid the slower battleships. Both ships complimented the other and both would have performed superbly in their intended roles. However, aircraft carriers revolutionized naval warfare and battleships became largely obsolete. The same traits that made the Montana superior to the Iowa class doomed it before it was even built. On the other hand, the unique design of the Iowa class allowed it to serve for several decades more.

As always, I hope you enjoyed the article. Feel free to leave a comment below. Also be sure to follow us on Facebook, Twitter, and Google+ to keep up with all the latest articles.




Chris Knupp

A student of military history, I am working to make history more interesting and accessible for everyone.


  1. Thanks so much for sharing all with the awesome info! I am looking forward to checking out far more posts! egeefdeekkegbade


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