Leyte Gulf: Japan's Battleship-Carriers
By Mike Bennighof, Ph.D.
April 2008

At the Battle of Midway in June 1942, the Imperial Navy lost four of its six fleet aircraft carriers. Shorn of these valuable ships, the Japanese high command desperately tried to replace them. Only one new aircraft carrier, Taiho, was under construction.

At the time, two large liners converted to aircraft carriers, Junyo and Hiyo, were just entering service. Many nations contemplated such conversions, and the Italian Navy had its similar Aquila. But the Japanese were not pleased with the results. The ex-liners had poor internal subdivision compared to a warship hull, their speed never matched design specifications, and hangar spaces were cramped. A converted warship would solve at least some of these problems.

Junyo soon after conversion, 1942

Casting about for warship hulls that could be converted to carriers fairly quickly, the Navy ordered work stopped on the new cruiser Ibuki, and her conversion to a carrier. The seaplane tenders Chitose and Chiyoda, designed with such an option in mind, got the same treatment. The incomplete battleship Shinano, third of the massive Yamato class, would also be completed as an aircraft carrier.

Naval engineers made a radical proposal: Convert all 10 of the Imperial Navy’s older battleships to aircraft carriers. Each could carry, they estimated, 54 aircraft. The high command removed the four Kongo class battlecruisers from the list, as these elderly but still fast ships would be needed to escort the rebuilt carrier forces. The admirals also vetoed conversion of the two battleships with 16-inch guns, Nagato and Mutsu.

Ise before her conversion

That left just four eligible dreadnoughts, two of the Fuso class and two more of the similar Hyuga class. Limited resources would have to be split between the conversions and new construction of the Unryu class about to be laid down in Japanese yards. A semi-conversion would instead be attempted, removing the aft armament and replacing it with a flying-off deck.

Approval came in June 1943, and worked started with Hyuga and her sister, Ise. The slightly older Fuso and Yamashiro, slated for the same work, never received the conversion. Their turret layout would have necessitated removal of six of their twelve 14-inch guns, where the Hyuga class would only lose four. And the pair converted were slightly faster.

Initial plans called for everything aft of the funnel to be removed, but the final version only removed the two stern turrets. A hangar took their place, with an aircraft handling deck above it. This was not a true “flight deck,” as aircraft were no longer intended to fly off of it. Two catapults would launch the planes.

The two ships initially were intended to carry the D4Y “Judy” dive bomber, which we described earlier. This plane had good offensive punch, but the battleships could not have recovered them: they would fly one sortie, then have to land at an airfield or on an actual carrier. Thus the battleships could not re-fuel or re-arm their aircraft, and would have to enter a port to recover them. Planners decided this was much too complicated, and wanted the two ships to be able to fully operate their air group.

Instead, the two ships would also operate the Aichi E16 Zuiun (“Auspicious Cloud”) seaplane, known to the Allies as “Paul.” Eleven of each type would be carried. The Auspicious Cloud carried a respectable bomb load and had good range and armament.

As a final modification, each ship received over a hundred 25mm anti-aircraft guns and a number of rocket launchers.

The two ships had disappointing careers as battleship-carriers. They participated with the First Carrier Fleet in the Leyte Gulf operation, and hundreds of American carrier planes swarmed the force, sinking all of its carriers but one. The massive firepower of the two battleship-carriers spared them. They undertook some transport missions in the last year of the war, but never appear to have actually operated their aircraft. American planes sank them at their moorings just before the war’s end, and both were scrapped afterwards.

Gamers of course are never satisfied with what was, and far more interested in what might have been. We’ve provided more rational air groups for the two ships. They would have been well-suited to operating the Ka-1 autogyro we detailed earlier.

With these craft on board, the battleship-carriers could have provided substantial anti-submarine capability. The aircraft handling decks would have been sufficiently large to handle both take-offs and landings. However, the Ka-1 was an army aircraft, and in Japan, Army and Navy did not cooperate.

Fleet air defense required fighters, and Japan had some very good seaplane fighters that could have been operated by the battleship-carriers. No other nation attempted to operate such planes by the 1940s, as the floats created such drag that it was believed no seaplane could come close to a land plane’s performance. Japanese designers first disproved this with a seaplane version of the A6M “Zero” fighter. While it did not equal the regular version of the plane, it wasn’t that far behind it. Requirements were issued for next-generation seaplane fighters.

In 1943, Kawanishi produced the N1K “Kyofu” (“Powerful Wind”), known to the Allies as “Rex.” The Powerful Wind, while not as good as contemporary land-based fighters, had surprisingly good performance for a seaplane. Kawanishi’s land-based version, the N1K1-J Shiden (“Violet Lightning”) was an excellent fighter, equal to the American Corsairs and Hellcats. These seaplnes would definitely have added to fleet air defense, though of course recovering them would have been far more cumbersome than carrier landings, especially in action.

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