Key Points and Summary – Japan’s unrealized “Super Yamato” (Design A-150) was Tokyo’s bid to dominate WWII at sea before U.S. industry fully mobilized.
-Envisioned at 90,000 tons, 27 knots, and armed with six 20-inch guns, it aimed to win a brief, decisive battle and frighten FDR into restraint.
-Reality intervened: the guns and propulsion were too heavy, shipyards lacked workers, sailors were scarce, and carrier aviation eclipsed the big-gun era. Competing needs—oil seizures, war in China, a vast army—drained resources.
-A-150 never left the drawing board, a cautionary tale that the Americans never had to face at sea.
-Its failure underscored Japan’s strategic overreach and misread technology.
Super Yamato Design A-160: What If Japan Had Built the Biggest Ship of World War II?
We are fascinated by American World War II battleships, such as the Iowa-class. No other US Navy vessel had such massive armor and firepower. However, don’t forget that the Japanese had their own Yamato-class of dreadnoughts, which were pound-for-pound able to match the US Navy in destructive power and survivability.
The Japanese were ambitious with their battleship program. There was a noteworthy plan to make the “Super Yamato.” Also known as the Design A-150, this vessel would have dominated the waves, giving Japan a significant advantage in maritime warfare, outgunning and outmanning any ship the Americans could deploy.
It Would Never Have Worked Out
The Super Yamato was doomed from the start. It never went beyond the planning stage as aircraft carrier warfare eclipsed the need for massive dreadnoughts. The maritime technology and human capital needed just never materialized for the Japanese.
Japan started the quest for the super dreadnought in 1938. This naval build-up made the Americans stand up and take notice that the Japanese could more than dominate their region with fast and capable ships. They could even use it to bring the fight to US shores and threaten naval bases in Hawaii and bully the West Coast of the country.
It Could Win the Mother Of All Naval Battles
This would be more than a tactical battleship. The Japanese sought a vessel that could significantly impact the warfighting capabilities of the US Navy and overwhelm it with heavy firepower and armor that would make it difficult to sink.
The Super Yamato would have not just four 16-inch guns, but six 20-inch guns to bring death and destruction to its enemies. Each ship of the class would displace a gargantuan 90,000 tons—twice the displacement of the Iowa-class. And the ships would be fast—able to steam at 27 knots.
Beat the Americans Before the Sleeping Giant Woke Up
Japan knew that if it was going to have a world-class fleet, it needed a capital ship that could quickly eliminate the US Navy before the Americans could gin up their defense industrial base. The production strategy was about speed for the Super Yamato. Produce as many as possible while the American giant slept.
The Design A-150 was then re-imagined as the best warship in the world. Engineers and designers started work on what was to be the most dominant battleship ever produced.
Japan had always envisioned a giant force-on-force naval battle that would be brief in duration and decisive in outcome. They based their naval strategy on the Russo-Japanese War at the turn of the century. The Japanese dominated the Battle of Tsushima in 1905 against the Russian fleet by quickly destroying six enemy battleships and 14 other escort vessels. If the Super Yamato could be produced, then the Japanese navy could create an ultimate victory without the need for a powerful army. Naval battle planners saw the Design A-150 as the straw that stirred the drink, and nothing was going to stop production—or so they thought.
Could Franklin D. Roosevelt Be Scared Into Submission?
The A-150’s bigger guns could simply eliminate as many American ships as possible to break President Franklin D. Roosevelt’s will to fight. The Japanese knew that the Navy was FDR’s favorite branch of the military. If the Japanese could frighten the president into submission, the Americans would simply surrender to Japan.
The Japanese thus depended on overall firepower with the Design A-150. This meant it would build the best and most powerful guns in the world. To accompany those massive 20-inchers, the builders installed huge 45-caliber 510mm guns in double and triple turrets.
The US Navy had nothing like the Super Yamato at the time. This was going to be a problem for the Americans, as the shipping industry was not geared towards building warships in large numbers.
However, the Japanese were just too optimistic about their own naval industrial base. The guns were too heavy. The battleship’s speed was not attainable with such a massive ship, and it was going to be difficult to make 90,000 tons go that fast. Engineers grew frustrated at the delays, and the imperial naval command threw up its hands.
There Were Just Too Many Military Needs for Japan
Also, the Navy wasn’t the only branch. Yes, the Japanese envisioned beating the United States by using only its maritime force. However, a large army was still needed to secure the natural resources required for military domination of the Indo-Pacific. Japan needed to seize oil fields in the Dutch East Indies. Moreover, there was a land war to be fought, and Japan sought to occupy China. This meant mustering a huge army that nabbed money and resources away from the navy.
The shipyards also lacked sufficient workers to build a fleet of Super Yamatos. Japanese interests were in a bind. Can the country build a navy and maintain a large army simultaneously? Even if the A-150 had been produced, there would not have been enough sailors to operate such a large ship, and aircraft carrier aviation was going to be a new trend that required a transformation in naval tactics, operations, and strategy. Naval aviation doctrine was in its infancy, and this would eclipse the need for such a large battleship.
Iowa-Class 5-Inch Guns. Image by Harry J. Kazianis/National Security Journal.
The Super Yamato was thus never produced. A huge battleship-to-battleship decisive battle never really came about. World War II was not going to be like the Battle of Tsushima, where the badly trained and poorly led Russian navy was defeated. The Americans were simply too good, and their shipping industry responded by producing a wide range of warships that the Japanese navy could not match.
So, the A-150 will be a footnote to history as a ship whose time never came. The Japanese had grand ambitions but little follow-through that would have produced the biggest and most powerful ship of World War II. The Americans had dodged a bullet and were thankful they never had to go up against the Super Yamato.
About the Author: Brent M. Eastwood
Brent M. Eastwood, PhD is the author of Don’t Turn Your Back On the World: a Conservative Foreign Policy and Humans, Machines, and Data: Future Trends in Warfare plus two other books. Brent was the founder and CEO of a tech firm that predicted world events using artificial intelligence. He served as a legislative fellow for US Senator Tim Scott and advised the senator on defense and foreign policy issues. He has taught at American University, George Washington University, and George Mason University. Brent is a former US Army Infantry officer. He can be followed on X @BMEastwood.
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