Why is a battleships’s underwater armor important? Battlewagons hurled big cannon shells at each other, not torpedoes, which is why battleships tended to be more heavily armored above the waterline.

But tell that to the German warship Bismarck, which was ultimately hunted down and sunk after a 14-inch shell from the British Prince of Wales landed short, dove through the water and penetrated the German battleship below her more lightly armored waterline.

As part of its quest for qualitative superiority, Japan trained its battleship crews in long-range shots to achieve such devastating underwater hits. “The chances of any given shell giving us a good underwater effect is pretty low,” Parshall tells War is Boring. “But if you throw enough shells up in the air, strange things can happen. And after a while, odds are, they probably will.”

It would have been the ultimate duel of dreadnoughts. In one corner, Japan’s Yamato, weighing in at 65,000 tons, the biggest battleship in history. In the other corner, Iowa, at 45,000 tons the pride of America's World War II battleship fleet. In reality, the two ships never met in battle. But what if they had, in a cataclysmic clash of seagoing titans?

One researcher can offer an answer, or at least a very educated guess. Jon Parshall, historian and author of the superb Shattered Sword: The Untold Story of the Battle of Midway has pitted the top battleships of various nations against each other at Combinedfleet.com, the go-to site for information on the Imperial Japanese Navy.

Among the battleships he compares are Yamato and Iowa, based on five criteria: guns, armor, underwater protection, fire control and “tactical factors” such as speed and damage control.

Guns

Yamato’s 18.1-inch guns were the largest ever mounted on a warship. Since they couldn't match American quantity, it was Japanese navy doctrine for each warship to be more powerful than its individual U.S. counterpart. Yamato’s nine 18-inchers could throw a 3,200-pound shell out to 26 miles, while Iowa’s nine 16-inch guns could propel a 2,700-pound shell 24 miles.

Even though Japanese shells were less effective than American ones, the range advantage should belong to Yamato. Yet the real issue was even hitting the target in the first place. Given World War II fire control systems, the chance of hitting a battleship moving at 30 miles per hour from a distance of 25 miles is very small.

For his analysis, Parshall assumes that both battleship captains would close the range to less than 23 miles. At that distance, both the Yamato’s and Iowa’s guns could penetrate each other’s armor. “That’s why I say there’s a lot of luck involved here,” Parshall tells War is Boring. “Iowa’s fire control is better. But if Yamato gets lucky and gets in the first hit or two, and they’re doozies, it could very easily be game over for Iowa.”

Advantage: neither ship.

Armor

Yamato seemingly had the edge here, with 16 inches of belt armor to Iowa’s 12 inches. The Japanese vessel had 9 inches of deck armor to Iowa’s 6, and an impressive 26 inches of armor on the faces of her main gun turrets, versus just 20 inches of turret armor for Iowa.

“Yamato was simply built to stand up to and utterly outclass any conceivable American or British opponent by sheer weight of gunfire and elephant-like armor,” Parshall writes. “As such, hers is a sort of ‘brute force’ approach to protection. Her armor layout isn’t the most efficient, but she has a lot of armor, so it doesn’t really matter.”

While Yamato was thickly armored everywhere, Iowa’s armor was thicker over her more vital areas. However, as Parshall points out, only America could afford to build battleships with hulls and interiors constructed entirely out of tough but light Special Treatment Steel, which meant that U.S. battleships could be smaller and lighter for an equivalent amount of protection.

Nonetheless, Parshall gives a slight edge to Yamato here; if both ships suffered damage to their fire control systems and had to close the range, the invulnerability of Yamato’s turrets to Iowa’s shells could prove important.

Advantage: Yamato.

Underwater protection

Why is a battleships’s underwater armor important? Battlewagons hurled big cannon shells at each other, not torpedoes, which is why battleships tended to be more heavily armored above the waterline.

But tell that to the German warship Bismarck, which was ultimately hunted down and sunk after a 14-inch shell from the British Prince of Wales landed short, dove through the water and penetrated the German battleship below her more lightly armored waterline.

As part of its quest for qualitative superiority, Japan trained its battleship crews in long-range shots to achieve such devastating underwater hits. “The chances of any given shell giving us a good underwater effect is pretty low,” Parshall tells War is Boring. “But if you throw enough shells up in the air, strange things can happen. And after a while, odds are, they probably will.”

Of the seven battleships Parshall analyzed, Yamato and Iowa had the best underwater armor. However, Yamato had poor seams between her upper and lower armor belts, which allowed water to enter when she was torpedoed by U.S. aircraft off Okinawa.

Advantage: Iowa.

Fire control

Marksmanship is a key consideration when trying to hit a moving target from 25 miles away, even one that is almost three football fields long. Here was perhaps the Iowa’s biggest advantage. Japanese fire control radar was poor, while American fire control radar was the best in the world.

“In a 1945 test, an American battleship (the North Carolina) was able to maintain a constant [fire control] solution even when performing back to back high-speed 450-degree turns, followed by back-to-back 100-degree turns,” Parshall writes.

“This was a much better performance than other contemporary systems,” he continues, “and gave U.S. battleships a major tactical advantage, in that they could both shoot and maneuver, whereas their opponents could only do one or the other.”

However, the Japanese had superb optical rangefinders and night binoculars, which enabled them to surprise and decimate the U.S. Navy in night battles off Guadalcanal. But optics were susceptible to bad weather and smoke.

“All optics do a very good job at determining bearing to the target, but not so good at determining range,” Parshall says. “World War II radar, on the flip, could give you a very good range number, but unless you had a modern set, getting a decent bearing was a real bear. So, the combination of decent optics plus world-class radar is way better than world-class optics plus crappy radar.”

Advantage: Iowa.

Tactical factors

Here Parshall lumps together several factors, such as speed and damage control. Iowa could sail at 33 knots to Yamato’s 27, which would confer some advantage in opening or closing range. Yamato had a displacement one-third larger than Iowa, which should confer a larger ability to absorb damage.

But when it comes to damage control, America was far ahead of Japan and other nations.

Advantage: Iowa.

And the winner is …

So which battleship would win? Based strictly on raw numbers, I would give the edge to Iowa based on her superior fire control. But it would only take a lucky hit or two to knock out a radar, and with those powerful 18.1-inch guns, a hit from Yamato’s main battery would hurt Iowa.

While both ships enjoyed certain advantages over each other, those advantages are so slender that luck would probably play as decisive role as firepower and armor.

Of course, this scenario is hypothetical, the province of armchair admirals and war gamers. Yamato and Iowa wouldn’t have stood turret-to-turret in an arena like a pair of heavyweight boxers. They would have been surrounded by cruisers, destroyers and subs.

In fact, the only time battleships slugged it out, without all the small fry in the way, was when Bismarck and the German cruiser Prinz Eugen confronted the British battleship Prince of Wales and the battlecruiser Hood in the Battle of the Denmark Strait.

In the end, a Yamato versus Iowa duel might have been a fascinating but futile curiosity. In 1945 the era of the battlewagon was already ending, sinking beneath the weight of swarms of aircraft. In fact, Yamato was sunk during its suicide run to Okinawa on April 7, 1945, overwhelmed by waves of U.S. carrier-based torpedo bombers.

Iowa enjoyed a career through World War II, Korea and was even reactivated during the 1980s. She bombarded shore targets aplenty, but never had the chance to engage an enemy battleship.

This first appeared in WarIsBoring here.