Midway:
Carrier Akagi, Part One
by Mike Bennighof, Ph.D.
September 2025

In 1917, the Japanese Diet finally approved a long-sought goal of the Navy Ministry: a fleet program known as Eight-Eight, providing for eight new modern battleships and eight battle cruisers. Most of the ships would carry 16-inch guns; the final four battleships would have even larger 18-inch guns. If the Imperial Navy could not match the Americans in quantity, it would do so with quality. Every ship must have superior fighting power to its American equivalent.

The two battleships of the Tosa class and two battle cruisers of the Amagi class were laid down in 1920, and two more battle cruisers in 1921 when the launch of previous ships cleared the slipways for them. Four more battleships and four battle cruisers were to follow in 1922, and together with the two Nagato-class ships already under construction, that would make up the authorized sixteen ships.

The 1922 Washington naval limitations agreement brought the program to a swift end. The two Nagato-class ship would be completed (following some controversy over the status of the second ship, Mutsu), and all of the others either cancelled (if construction had not begun) or scrapped (if it had). The agreement did allow for two capital ships to be converted into aircraft carriers, and the Japanese selected the incomplete battle cruisers Amagi and Akagi.

As a battle cruiser, Amagi would have been a huge ship: 41,000 tons’ displacement, carrying ten 410mm (16.1-inch) guns and making 30 knots. She would have a mix of oil- and coal-burning boilers, and typically for Japanese battle cruisers, insufficient armor to withstand her own main guns. But she would be more than adequate for her primary task, to overcome the American Lexington-class battle cruisers (much faster ships, with thinner armor and fewer guns).

Yokosuka Naval Arsenal, 3 September 1923, two days after the Great Kanto Earthquake. The wrecked battle cruiser Amagi is at dead center.

Japan signed the Washington accords in February 1922, and design work began on the aircraft carrier conversions, with the Diet approving a hefty financial package to cover the alterations, which would result in much more expensive ships than the battle cruisers (not even counting to cost of their aircraft). Construction had not begun on either ship when the 8.2-magnitude Great Kanto Earthquake struck the Tokyo region on 1 September 1923.

Akagi, still on the slipway at Kure Naval Arsenal, roughly 640 kilometers from the quake’s epicenter under Sagami Bay, suffered no serious damage. But Amagi, also on the slipway at Yokosuka Naval Arsenal, was but 30 kilometers away. The moving earth twisted the hull brutally, collapsing part of it and damaging Amagi beyond repair. She would be scrapped on the spot.

The Imperial Navy needed a replacement. The other two Amagi-class battle cruisers, Takao and Atago, had barely progressed beyond the keel-laying stage when construction halted; they had been laid down on the slipways where the battleships Tosa and Kaga had been constructed, and construction could not begin until those two ships had been launched. What steel had been erected for the two battle cruisers had long since been dismantled. That left the two incomplete battleships. Tosa had been moved from Nagasaki to Kure in August 1922, where she still lay incomplete. Kaga likewise had remained at the Kawasaki shipyard in Kobe, as the Imperial Navy dragged its feet on scrapping the pair. In December 1923, the decision became formal: Kaga would replace Amagi, and Tosa would be expended in tests

Akagi on her first sea trials in the Inland Sea, 17 June 1927. She’s not on fire; that’s her usual exhaust output before reconstruction. .

Actual work on Akagi would not begin for another two years. Early design sketches actually gave the carrier a single, flush flight deck and an island on the deck’s starboard side, but could not find a good answer to the gigantic funnel needed by the ship’s huge power plant. The architects finally chose a layout drawing heavily from the British carrier Furious, with three separate flight decks. The upper deck was a conventional flight deck, and the lower deck a “flying-off” deck that allowed small aircraft to roll right out of the lower hangar and take off. The middle deck, though called a “flight deck,” instead housed the ship’s bridge and two twin turrets for 20cm (7.9-inch) guns; while it had been intended that lightweight planes could take off there, no one seems to have been brave enough to try it with just 15 meters to get up to flight speed. Throughout her service life, Akagi never carried a catapult.

Six more 20cm guns occupied casemate mounts near the stern; at the time, most planners thought that carriers would have to engage enemy cruisers in battle, and the treaty allowed a carrier to ten such weapons. The initial anti-aircraft suite consisted of a dozen 120mm Type 10 anti-aircraft guns in six twin mounts, three on either side of the flight deck, but mounted low enough that they could not fire across the deck. The design team solved the problem of the funnel with an innovative curved design that directed exhaust gases down and away from the flight deck. This odd funnel would be sprayed with seawater during flight operations, to reduce and cool the exhaust. A second, smaller funnel stood straight up. With less space given over to the exhaust, Akagi could carry 60 planes. She retained her mixed coal- and-oil fired boilers, giving her an output of 133,000 horsepower, good for 31 knots. The Imperial Navy, following its usual practice, officially claimed a top speed of 28 knots for her, and greatly understated her length (232 meters official, 261 meters actual) and displacement (28,000 tons official, 36,500 tons actual) as well.

Akagi commissioned in March 1927, and after shakedown spent most of her time training pilots in carrier takeoffs and landings, and working out carrier procedures. Her third captain, Isoroku Yamamoto, put his emphasis on training rather than keeping an attractive ship. Reprimanded by his squadron commander, the future chief of the Combined Fleet came back with, “A warship is not a barber shop, and painting it is not the crew’s purpose.”

Some idea of the ship’s sheer size. Akagi (top) and battleship Nagato, seen at Yokosuka, 15 August 1930.

The silhouette of the triple-decked Akagi became iconic throughout Japan; during this period, the Imperial Navy had not yet adopted its later penchant for extreme secrecy. But the lower flight decks proved useless in practice, and with heavier aircraft coming in the very near future, Akagi went to Sasebo Naval Arsenal in November 1935 for major reconstruction.

She would remain in dockyard hands for just over three years; financial pressures brought on by the Great Depression slowed the work. The forward flight decks, gun turrets and bridge were all removed, and the main (now only) flight deck extended to just short of the bow. The deck had a slight incline, of 1.5 degree up from the stern to amidships, and 0.5 degrees up from the bow.

The mixed-firing boilers gave way to a purely oil-fueled power plant, which helped reduce the massive flow of smoke. The upright funnel went away, with all uptakes now trunked into a single, down-turned funnel on the ship’s starboard side. The former coal bunkers became additional crew quarters, while the new main hangar extended the full length of the ship (right under the flight deck), with a second hangar deck of the same size immediately below. A third, much smaller lower hangar deck held dis-assembled aircraft, to serve as replacements. Three elevators served the two main hangars.

The re-design retained some design flaws, and also introduced new ones. The tanks for aviation gas were embedded in the ship’s structure, which meant that if Akagi suffered a shock (from perhaps a bomb or torpedo hit), it would be transmitted to the gas tanks, possibly causing cracks or even ruptures. Akagi’s original battle cruiser design came from an era when naval architects preferred very rigid structures, not yet understanding how a shock could be transmitted through steel. That made her much more vulnerable to the shock-wave from a near-miss than was understood at the time.

Akagi after modernization. Seen at Sukumo Bay, 27 April 1939.

Japanese practice called for planes to be armed and fueled in the hangars, which were enclosed (though not protected by armor, nor was the flight deck) and therefore quite capable of trapping the gas vapors from damaged tanks. The planes would be lifted to the flight deck and warmed up there; carriers with open hangars could do that in the hangar, greatly speeding the readiness cycle.

Enlisted sailors despised Akagi. Crew quarters had been an afterthought, and the reconstruction had simply stuck them, and other new compartments, in any available space. This created a rat’s warren of narrow passages below decks, a maze with no particular rhyme or reason, and no one seemed to have an accurate map of them. The crew had to just learn.

The massive flow of smoke out of the new, single down-turned funnel made it impossible to open the portholes along the starboard side of the ship, aft of the funnel. That section of crew quarters quickly received the name “Murder Flophouse.” Sailors contracted tuberculosis and suffered from dysentery. Attempting to escape the hellish conditions of heat and stagnant air, they strung their hammocks in passageways and on the hangar decks. The ship showed signs of having been built by the low bidder on a government contract: sloppy application of waterproofing to the flight deck’s wooden planks left hardened gobs of black residue.

Akagi did offer, most crewmen agreed, excellent meals.

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• Journal 42: Battleship-Carriers

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Mike Bennighof is president of Avalanche Press and holds a doctorate in history from Emory University. A Fulbright Scholar and NASA Journalist in Space finalist, he has published a great many books, games and articles on historical subjects; people are saying that some of them are actually good. He lives in Birmingham, Alabama with his wife and three children. He misses his lizard-hunting Iron Dog, Leopold.

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