Yamato vs. Iowa: Putting the Debate to Rest

yamato vs. iowa

yamato vs. iowa


yamato vs. iowa

Yamato vs. Iowa. The debate that has raged on for years. No topic has divided naval history lovers more than this. It shouldn’t come as a surprise that the biggest war machines ever created would generate the biggest arguments. However, its time to put that argument down once and for all. Being no stranger to controversial topics, I will attempt to settle this argument.

I could simply just guess which ship would win a hypothetical battle with the other. However, World War II was not decided by combat between battleships. It was decided by fleets made up of various ships. With that in mind, I am going to solve this debate through another method. I am going to examine how each ship contributed to the fleet. What advantages did it provide, what disadvantages, and how it contributed to the fleet.

So lets examine each ship and determine which one was the more successful battleship. It is time to settle the Yamato vs. Iowa debate once and for all.


Big guns are the defining trait of the battleship. As battleships advanced, their guns got bigger and more destructive. Both the Yamato and the Iowa had the largest guns of their respective nation. Let’s take a look at what advantages these guns provided.

Yamato Anti-Surface Firepower

yamato vs. iowa

The primary armament of the Yamato was the 40cm/45 Type 94, however the name was intentionally misleading. These cannons were actually 46cm or 18.1″ in. They were the largest cannons ever mounted on a battleship. Firing a powerful 3200lb shell out to 26 miles, they were capable of penetrating all other battleships at most combat ranges. The Yamato was designed to slug it out with any battleship afloat and come out victorious. Had naval engagements been solved solely through battleships, the Yamato probably would have been a success.

yamato vs. iowa12.7cm Type 89 onboard a Japanese seaplane tender. Yamato carried 12 of these mounts for a total of 24 barrels at the end of her career.

Supporting her massive cannons was a collection of smaller guns. Originally, the Yamato was laid down with 12x 12.7cm dual purpose guns and 12x  heavier 15.5cm guns. Her 12.7cm guns could fire at 14 RPM before rapidly dropping to a 8 RPM sustained. Her larger 15.5cm cannons could fire at 5 to 6 RPM and to a range of 22k yards. Later on in her career, the Yamato had her amidships 15.5cm guns removed and 12x more 12.7cm guns added to increase her anti-air firepower.

By 1945, Yamato’s anti-surface armaments were as follows:

  • 9x 46cm Type 94
  • 6x 15.5cm 3rd Year Type
  • 24x 12.7cm Type 89

An examination of Yamato’s Anti-surface firepower would be broken down as such:

  • 46cm Firepower Weight: 28971 lbs. per broadside 
  • Secondary Battery Firepower weight (sustained rate): 12.7cm Type 89 – 9734 lbs. per minute / 15.5cm 3rd Year Type –  3696 lbs. per minute
  • Total Anti-Surface Firepower Weight: 42401 lbs. per minute (With a single broadside)


Iowa Anti-Surface Firepower


yamato vs. iowa

While the US tested larger cannons, they armed the Iowa class with the proven 16″ cannon but of a new design. The 16″/50 Mark 7 was a light weapon for its size and it was soon made more powerful with the introduction of the Mark 8 “super heavy” armor piercing shell. Using the mark 8, the Iowa class nearly rivaled the Yamato’s larger 18″ cannons at long ranges. The guns were accurate, powerful, and gave stellar service throughout their careers.

yamato vs. iowa

Supporting her main armament was 20x smaller 5″ dual purpose guns. These were modern, effective guns used on virtually all US Warships during the Second World War. They could send a 55lb shell over 17,000 yards at rates exceeding 20 RPM, though sustained rates were often around 15 RPM.

The anti-surface armaments of the Iowa were as follows:

  • 9x 16″/50 Mark 7
  • 20x 5″/38 Mark 28

An examination of Iowa’s Anti-surface firepower would be broken down as such:

  • 16″/50 Mark 7 Firepower Weight: 24,300 lbs. per broadside
  • Secondary Battery Firepower Weight (sustained rate): 16,554 lbs. per minute
  • Total Anti-Surface Firepower Weight: 40,854 lbs. per minute (With a single broadside)


Who had the Better Anti-Surface Firepower?

Despite the Iowa’s powerful shells, she could not overcome the massive cannons of the Yamato. Some might argue that radar would allow Iowa to attack ships from longer ranges. However, radar directed gunfire at long range was still in its infancy. On the other hand, the Yamato was equipped with excellent optics that could accurately cover the normal combat ranges for battleships at that time. The argument could be made that the Iowa was able to just as easily dispatch any warship afloat during WW2 as the Yamato. However, an advantage is still an advantage and the Yamato offers better primary firepower if only slightly.

When secondary weapons are added however, the battleships are much closer. Iowa’s modern 5″/38 outmatch their contemporaries with a much higher rate of fire. When defending itself or other ships from hostile destroyers or other small warships, the Iowa might offer slightly better protection. Against larger, more heavily armed ships, the Yamato’s combination of 46cm and 15.5cm guns would certainly be more beneficial.

As far as anti-ship firepower is concerned, the Yamato wins this one.


Yamato Anti-Air Firepower

If it was simply the number of guns that won this battle, then at first glance the Yamato would appear the clear winner. However, a closer look at the anti-air weapons reveals a different outcome.

While the Yamato was armed with 162x 25mm guns and 4x 13mm guns, these were outdated, inefficient designs. For instance, while the Type 96 25mm boasted a maximum rate of fire of almost 260 RPM, they never achieved that level of fire in combat. Bulky 15 round magazines had to be constantly reloaded and the entire gun had to cease fire to allow magazine to be changed. This lowered the practical rate of fire to roughly 110 RPM. Her heavy 12.7cm guns were also outdated and suffered against the newest aircraft at the time.

Yamato class Anti-Anti Firepower Weight:

  • 162x 25mm Type 96 – 9801lbs per minute
  • 4x 13mm Type 93- 109lbs per minute

Total AA Gun Firepower Weight – 9910lbs per minute 

  • 24x 12.7cm Type 89 Firepower Weight (Sustained) – 9734lbs per minute

Total Firepower Weight – 19,644lbs per minute

Iowa Anti-Air Firepower

Unlike the older weapons on the Yamato, the Iowa had no such issues with her AA weapons. While her 20mm Oerlikons also had to cease fire to replenish ammo, they benefited from a larger magazines that were easier to change. Iowa’s biggest advantage lay with her 40mm Bofors. These guns had the benefit of continuous fire. Clips were inserted into the top of the weapon and the gun itself never had to stop firing so long as it didn’t overheat. Her large 5″ guns were modern and had the benefit of high rate of fire and superior shells.

Iowa class Anti-Air Firepower Weight:

  • 80x 40mm Bofors – 19,056lbs per minute
  • 49x 20mm Oerlikons – 3652lbs per minute

Total AA Gun Firepower Weight – 22,708lbs per minute

  • 20x 5″/38 Mark 28 Firepower Weight (Sustained) – 16,554lbs per minute

Total Firepower Weight – 39,262lbs per minute


Who Had the Better Anti-Air Firepower?

For anti-air firepower, the Yamato doesn’t even come close to the Iowa. Furthermore, the numbers I calculated for the Iowa are on the conservative side. During combat the 5″, the 40mm, and the 20mm weapons all have been recorded firing at much higher rates. I chose numbers at the lower end of the scale to ensure both ships are represented more accurately. Even so the Iowa has over 50% more anti-air firepower than the Yamato.

Not only does the Iowa completely dominate the Yamato in anti-air performance based on firepower weight, but it also dominates in effectiveness of firepower. The 40mm Bofors were placed on modern mounts with superior gun sights and the ability to easily track the fastest fighters of World War 2. By comparison, the 25mm Type 96 lacked the range and the ability to track fast aircraft.

The Iowa had more anti-air firepower and the ability to use it better. In this category the Iowa reigns supreme.


Fleet Flexibility

Fleet flexibility is the term I will use to determine how well our warships interact with their respective fleets as far as mobility is concerned. Being able to not only keep up with the fleet, but support them is crucial for any warship. During World War II, battleships were no exception to this rule as they were frequently used as heavy escorts. We will examine the flexibility of the Yamato and the Iowa by looking at their speed and endurance.


As fleets became more important, the speed of individual vessels became equally important. Vessels that could not keep up could not contribute to the defense of the fleet or its offensive power. If the fleet was forced to reduce speed to allow slower vessels to keep pace, they hamper their own ability to fight.

The Yamato, while considered by some to be a fast battleship, was anything but fast compared to her supporting ships. Her 150,000shp plant could push her bulk up to 27 knots, a respectable speed, but slower than other modern battleships. Her slow speed severely hampered her ability to keep pace with Japanese carriers. Likewise, her speed required escorts to keep pace with her. This effectively meant that any operations with carriers would effectively break the fleet in two. An example of this can be seen during the Battle of Midway, where the slower speed of the battleship group prevented them from keeping up with the carriers, robbing them of crucial protection.

yamato vs. iowa

The USS Wisconsin escorting several carriers in the Pacific. The high speed of the Iowa class allowed them to keep pace with carriers and protect them.

The battleships of the Iowa class were a unique exception to traditional battleships. For them, speed was as important as firepower and armor. To provide this high speed, the Iowa class was powered by a large 212,000shp plant. Compared to other battleships, the Iowa was blisteringly fast with the ability to steam at speeds greater than 32 knots. This allowed her to easily keep pace with carriers and other warships and provide them with heavy anti-air firepower.


Endurance describes the range or a warship of the distance in which it can travel on its own fuel.

The Western side of the Pacific is littered with islands. Japan intended to establish a ring of bases on the outermost islands while interior islands would serve to refuel and resupply their ships. The idea that ships would be operating relatively close to supply points caused the Japanese to place less focus on the endurance of their ships. The Yamato could steam for only 7200 nautical miles at 16 knots. This would not have been an issue had Japan been able to establish adequate supply lines, but as supplies dwindled it became a big disadvantage. Furthermore, she was known as a notorious fuel hog. During much of 1942 she laid idle at Truk as Japan could hardly afford to fuel her, leading troops ashore to call her “hotel” Yamato. I would think that lack of fuel and other supplies takes most of the blame, but its still a disadvantage if the Yamato squanders what little fuel is available.

yamato vs. IowaYamato and Musashi at Truk in 1943. To soldiers ashore this was a common sight at the time. The Imperial Navy had to carefully choose which ships to use and the Yamato vessels were often left behind. 

Across the Sea, the US Navy was well aware of the need to fight across the vast reaches of the Pacific ocean. Considerable effort was made to increase the range of warships and the Iowa was no exception. At a speed of 15 knots, the Iowa class could steam for over 14,000 nautical miles. This allowed the Iowa more freedom as it wasn’t tied down by refueling vessels. Freedom from long supply lines is an enormous advantage that the US Navy took advantage of. The Iowa could operate for long periods on their own vast fuel reserves, allowing oilers to resupply other ships of the fleet. In fact, the copious amounts of fuel carried by the Iowa battleships allowed them to act as armored fueling depots for their own escorts. This little known advantage was appreciated by naval strategists and actually influenced future ship designs.

yamato vs. iowa

The USS Massachusetts refueling two destroyers. The large amounts of fuel carried by US battleships allowed them to replenish their own escorts. This improved not only thier own endurance but that of their escorts as well. 

Who Has the Better Fleet Flexibility

In this category, the Iowa is the clear winner. High speeds and long range ensured that she could go wherever the fleet could. She could also help to fuel other ships in the fleet. In contrast, the Yamato was hampered by slow speed and inferior range. She could hardly keep up with other ships, much less afford to fuel them from her own stores.

Yamato vs. Iowa: Final Conclusion

So in the Yamato vs. Iowa debate, which was the better battleship? Not in the one on one battle that everyone seems to think they would have fought, but as components of a fleet.

Based on which ship offered more to the fleet, the main strengths of the Yamato are of little use.  In the anti-surface role, the Iowa might have been slightly inferior to the Yamato. However, aircraft carriers were the primary offensive power at the time so Yamato’s advantage is of dubious value. Yamato’s thicker armor is of little benefit as the primary threats at that point were submarines and aircraft. In these particular areas the Iowa could survive everything the Yamato could.

In areas most important to supporting the fleet, the Iowa soundly beats the Yamato. It has the range to keep pace with the carrier forces and operate across the entirety of the Pacific. Its fast enough to support allied ships and chase down enemy ships. Last but not least, it offers over 50% more anti-air firepower than the Yamato, an important attribute at a time when naval airpower was dominant. The Iowa was designed to go beyond the traditional battleship roles.

Of course, the battleship was in its hour of twilight during World War II. However, the Iowa offered up just enough to remain relevant unlike older dreadnoughts like the Yamato that were designed for a style of combat long gone.

If I were an admiral and I had the choice of choosing the Yamato or Iowa to support the fleet, sign me up for the Iowa every time.

yamato vs. iowa

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Chris Knupp

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


  1. your calculations are slightly off, any surface ship of the time could not bring all of it’s secondary armaments to bear in a broadside. at most maybe ½ could fire from either port or starboard. but it is the same for either the Iowa class or the Yamato class. Same is true to some extent for AA dedicated weapons except some are in more flexible positions.

    • You are absolutely right. However, I kept it simple and went for the general overall number rather than break it down any further. I will do a more detailed comparison after awhile.


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