The Emperor’s Sword:
Japanese Battleships, Part One
By Mike Bennighof, Ph.D.
January 2024

Second World War at Sea: The Emperor's Sword is our Pacific theater equivalent to Plan Z, a massive expansion set stuffed with ships and planes that only existed as drawing-board proposals, with an alternative-history story sending them into action in thirty new scenarios. While the Long War story arc (the one including both The Emperor’s Sword and Plan Z) concentrates on cutting edge technology of the 1940’s with aircraft carriers and eventually jet aircraft, it’s also home to battleships. Giant battleships armed with huge guns.

Unable to match the Americans ship-for-ship, the Imperial Japanese Navy bet heavily on the individual superiority of their new battleships. Yamato and her four sisters would be much larger than any other ship, existing or planned, with bigger guns – and new ships with even bigger guns would follow her. Still more huge battleships came off the drawing tables of the Imperial Japanese Navy’s Technical Department. Japan as she existed in our world lacked the resources to build them all, but that’s not the case in our alternative history.

Let’s have a look at the big new Japanese battleships of The Emperor’s Sword.

Tosa Class

The Tosa class began as an improved version of the preceding Nagato class battleships, incorporating some of the early lessons drawn from the Battle of Jutland to improve her armor scheme with thicker armor on her main deck and around her turrets, barbettes, and magazines. At the same time, a vastly-improved new boiler design allowed the ship to draw more horsepower from 12 boilers than Nagato had from 21. That savings in weight and space allowed fitting of a fifth twin turret, giving the ship a main armament of ten 410mm (16.1-inch) guns.

Both Tosa and her sister, Kaga, would be sacrificed as part of the Washington naval accords of 1922, in which the Americans used intercepted telegrams to roll the Japanese negotiators. Kaga became an aircraft carrier, while Tosa became a floating target.

In our alternative history, both would be completed on schedule (late 1922 and early 1923), and modernized in the 1930’s, with their four mixed-firing boilers replaced by oil-burning installations. The twenty 140mm Type 3 secondary guns would be cut back to twelve, and a dozen 127mm Type 89 anti-aircraft guns, the standard such weapon for Japanese battleships and heavy cruisers, fitted in six twin mounts.

In this alternative history, Kaga is completed as a battleship and never converted into an aircraft carrier, as occurred in our own history. Tosa and Kaga are fast and powerful ships, considering their age, but they are among the lightweights when compared to later Japanese battleships.

Kii Class

For the next class of battleships, the Imperial Japanese Navy chose to merge the battleship and battle cruiser types into a fast battleship. The Kii-class battleships greatly resembled a more heavily-armored but not quite as fast version of the Amagi-class battle cruisers (which do not appear in The Emperor’s Sword in battle cruiser form – all four been converted into aircraft carriers). They had the same main armament as Tosa, with four fewer 140mm guns in their secondary batteries, but were expected to be three knots faster than the previous battleship design, clocking just a hair below 30 knots.

Four of them were projected, but contracts had only been awarded for the first two ships when all of them were cancelled in late 1922. They would have been laid down on the slipways vacated by the Amagi class, with completion expected in 1925.

In our alternative history, all four are completed, and modernized in the 1930’s like Tosa and Kaga. Designed from the start for oil fuel, Kii and her sisters could keep their power plant, but they would receive the same improvements to protection and armament as Tosa. They are fast enough to accompany carrier task forces, and in the world of the Long War this is their primary task.

Mino Class

These ships never received formal names, and are usually called “Number 13” in the literature. They would have followed the Kii class, as enlarged versions with a huge power plant making 150,000 horsepower to drive them at 30 knots. Once again, the building program called for them to be laid down on the slipways used for the previous class; most sources place this in 1922 but it’s highly unlikely that Kii and her sisters would have been launched by then. The projected completion date of 1927, on the other hand, seems more reasonable.

The big change for the new class would be their main armament: eight 460mm (18.1-inch), 50-caliber rifles in four twin turrets. That would give them massive firepower, as well as great range, and with their speed they could dictate the range of battle against virtually any conceivable opponent. Armor would likewise be much thicker than Kii and Tosa, but contrary to American practice the new ship would not be invulnerable to her own weapons.

Thanks to yet another technological advance, this time in turbine design, Number 13 was expected to displace slightly less than Kii despite making an incrementally better speed and carrying thicker armor. She would displace 47,500 tons, compared to 48,500 for Kii, and make 30 knots compared to 29.75. Outwardly, though, she would be a much larger ship: 915 feet long compared to the 826-foot Kii and 768-foot, 44,200-ton Tosa. Even Yamato “only” came in at 867 feet long, though the super-battleship was much beamier (and slower) with a far greater displacement.

In our history, all four projected ships would be cancelled before any contracts had formally been awarded, though shipyards had been assigned. In the alternative history of the Long War, this far more powerful Japan built and completed them as scheduled; they received a minor refit alongside the other older battleships’ more thorough reconstructions, losing four of their 140mm secondary guns and receiving a suite of twelve 127mm anti-aircraft guns in six twin mounts, plus a wide array of light anti-aircraft weapons. Unlike the other older battleships, which lost their torpedo tubes during their re-construction, those intended for the Mino class were removed before completion.

These fast, powerful ships serve, like the earlier fast battleships, as carrier escorts. They’re capable of driving off or destroying any conceivable surface threat to the carriers, with the speed to keep up with the flattops. Japanese carrier doctrine in the world of the Long War is no better-developed than in our own, at least at the start of the war, and so the huge battleships are not yet expected to provide anti-aircraft fire to defend the carriers – that will come later. It’s still a case of every ship for herself.

The next class would follow a far different design philosophy, outline and hull form, that would eventually lead to Yamato and her successors. We’ll look at those in our next installment. These three classes also see action in yet another reality, the Second Great War alternative history. But that’s another story.

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