Carrier Evolution VII: Early Japanese

USN Carrier Evolution VII: Early Japanese carriers

Seventh article in a series by Scot MacDonald. Reprinted with permission: Naval Aviation News, October 1962 pp. 39-42.

“In the last analysis, the success or failure of our entire strategy in the Pacific will be determined by whether or not we succeed in destroying the U.S. Fleet, more particularly, its carrier task forces.” ADML Isoroku Yamamoto, IJN, 1942.

“I think our principal teacher in respect to the necessity of emphasising aircraft carriers was the American Navy. We had no teachers to speak of besides the United States in respect to the aircraft themselves and to the method of their employment … We were doing our utmost all the time to catch up with the United States.” FADM Osami Nagano, IJN, 1945.

By Christmas Eve 1921, the Washington Disarmament Conference had already been going on for a month and a half. Participating were Great Britain, Japan, France, Italy, and the United States. It was on this day that Great Britain refused any limitation on auxiliary vessels, in view of France’s demand for 90,000 tons in submarines. The delegates then began to consider confining the treaty to capital ships and aircraft carriers.

Washington Treaty

The Washington Naval Treaty, signed February 6, 1922, established a tonnage ratio of 5-5-3 for the capital ships of Great Britain, the United States, and Japan, respectively, assigning a smaller tonnage to France and Italy. The same ratio for aircraft carriers was set, with an overall limitation of 135,000 tons each for Great Britain and the U. S., and 81,000 tons for Japan. It also limited any new carrier to 27,000 tons, with a provision that, if total carrier tonnage were not thereby exceeded, nations could build two carriers of not more than 33,000 tons each, or obtain them by converting existing or partially constructed ships which would otherwise be scrapped by the treaty.


HIJMS Hosho, was the first purpose-built aircraft carrier ever to be commissioned, 27 December 1922, 17 months before HMS Hermes. The temporary island was removed after her initial trials. The 168 x 18 x 6.7 metres hull displaced 10,500 tons at full load. The 30,000 hp engines, powered by geared turbines and 16 boilers, drove the ship at 25 knots. With a crew of 550, she carried 26 aircraft. She served in support of the Battle of Midway, with nine obsolescent B4Y1 torpedo bombers, but was not hit. After WW II, Hosho (photo right in October 1945) repatriated Japanese nationals.

December 27 that year, Japan commissioned its first aircraft carrier, the Hosho (Flying Phoenix). This was a remarkable hoku bokan (literally, mother ship for aircraft). Though the British were the first to operate aircraft onto and off a ship especially designed for that use, their first aircraft carriers were conversions. Hosho was a carrier from the keel, the first of its kind completed in any navy of the world.

Hermes contemporary

Laid down in 1919 at the Asano Shipbuilding Co. of Tsurumi, the ship was fitted out at Yokosuka Navy Yard at a standard displacement of 7470 tons, a speed of 25 knots, with the capability of handling six bombers (plus four reserve), five fighters (in addition to two in reserve) and four reconnaissance planes, a total of 21 aircraft.

Hosho was indeed a strange looking craft. She was all flying deck. Originally, she had an island structure and a tripod mast, but either because of the small width of her flying deck (and its attending hazards) or because some turbulence might have been caused by it, the island was taken off. The carrier sported three funnels on the starboard side. These were of the hinged type, held upright when not in use, and swung outboard to provide additional safety from stack gas. Later, they were placed in a fixed position, bending aft and slightly downward.

Hosho‘s original armament consisted of four 14 cm (five-inch) single mount guns and two 8 cm (three-inch) single mount high angle guns. At the outbreak of WW II, her high angle guns were replaced by four 25 mm twin mount machine guns. Later, the 14 cm guns were removed and 25 mm double or single mount machine guns were added.



The Nakajima A1N Gambet, Navy Type 3 Carrier Fighter, was in Japanese naval service from 1929 to 1935. Developed from the British Gloster Gamecock, its final version, the A1M2, had a 450 hp engine, a top speed of 150 knots and carried two 7.7 mm machines guns. It also had a 200-mile range with two small 30 kg bombs.

Japanese names

Before continuing with Japanese development, an explanation of the naming of their aircraft carriers is in order.

“Transliteration of the names of Japanese aircraft carriers into American equivalents is a pretty risky business,” said Roger Pineau, a frequently published writer on the Japanese Navy after World War II. “It becomes misleading. The names should be treated as such and should not be taken too literally. For instance, when we speak of astronaut Carpenter, we don’t visualize a man walking around with hammer and saw in hand.”

Chris Beilstein, another expert on Japanese aircraft carriers, concurs. “The Shokaku becomes ‘Flying Crane,’ for that is the closest we can translate the original Japanese. The first Japanese CV’s carried names of mountains and provinces. These, in turn, were frequently named after mythological characters. Shokaku, for example, could have been a flying crane in an age-old story, a crane that was named Shokaku. This is very much like our real life Misty, the wild horse. Certainly, to translate ‘Misty’ to literal Japanese would be meaningless to them, or at best, misleading. It would be more accurate to translate it ‘Wild Horse.’ Thus, ‘Misty,’ to the Japanese, would mean ‘Wild Horse,’ just as we would erroneously translate Shokaku as ‘Flying Crane.”

Japanese Naval Aviation dates back to 1912 when the Navy sent officer trainees to the USA, Great Britain, and France. They returned from France with two Farman seaplanes, and from the USA with two Curtiss seaplanes. A beach on the west side of Tokyo Bay, Oppama, was selected as a site for a seadrome in the fall of that year and placed into commission. The first class at Oppama consisted of four officers and 100 men.

The first landing on the Hosho was made by a British civilian, a Mr Jourdan, on February 22, 1923. (In chronological comparison, Eugene Ely landed on a platform on the armoured cruiser USS Pennsylvania January 18, 1911; USS Langley, the USN’s first aircraft carrier, a converted collier, was commissioned March 20, 1922; the first USA aircraft carrier built as such, from the keel, USS Ranger, was not commissioned until June 4, 1934.)

Akagi, a converted battlecruiser in the 1928A naval expansion program, decided upon in 1920, was completed by March 1923. Under the limitations set by the Washington Naval Treaty, Japan turned her attention to the conversion of the battlecruiser (then eight months under construction at the Kure Naval Arsenal). This, in 1928, became Japan’s second aircraft carrier, the Akagi (Red Castle, actually the name of a Japanese mountain). Akagi displaced over 30,000 tons standard when completed, had a speed of 31 knots, and carried 60 aircraft. She was armed with ten eight-inch and 12 4.7-inch guns.



HIJMS Akagi, Japan’s second aircraft carrier, seen here in 1928, was reconstructed in 1935-38 with a full-length flight deck, port-side island and increased aircraft complement, from 60 to 91. She was VADM Nagumo’s Pearl Harbour flagship, before contributing to a highly profitable Indian Ocean raid, dusting up Darwin as she passed by, 19 February 1942, and sinking the carrier HMS Hermes, two RN cruisers and HMAS Vampire off Sri Lanka (Ceylon) in April. Akagi was lost at Midway, 4 June 1942, after one bomb hit and internal AVGAS (aviation gasoline) explosions.

A sister ship, the Amagi (Heavenly Castle), was also scheduled for conversion at that time, but sustained severe damage in the earthquake of 1 September 1923. She was scrapped in July 1924 at Yokosuka. In her place, Japan converted the Kaga (the name of an old Japanese province) to an aircraft carrier. Originally, she was laid down as a 39,000-ton battleship, but was scheduled for the scrap pile as a result of agreed disarmament limitations. Conversion was completed in 1928 and she was commissioned the following year.



Akagi launches a D3A-1 (Val) dive bomber for the 19 February 1942 raid on Darwin.

The 1929 Japanese Year Book states, of Akagi and Kaga: They are the pride of the Japanese Navy, and though slightly inferior to the Saratoga of the USN in respect of speed, the Akagi surpasses the other in point of the range of her high angle guns, of which she carries 12 4.7-inchers. The Hosho … [is] by far smaller than the Akagi, but in the mode of construction [it possesses] special features of [its] own. The completion of the Kaga, only second to the Akagi, is a powerful addition to the Japanese Navy.

Kaga was reported as displacing 26,900 tons standard, but actually displaced over 30,000 tons, had a speed of 27 knots and carried 60 aircraft.



HIJMS Kaga, converted from a battleship hull, is seen here after major reconstruction (lengthened flight deck, completely re-engined, starboard side island) in 1936. She was at Pearl Harbour and contributed to the Darwin raid on 19 February 1942. Kaga missed the Indian Ocean sortie after running aground at Palau, 9 February 1942. She too was lost at Midway, 4 June 1942, after four bomb hits and internal AVGAS explosions.

London Treaty 1930

As the signatories of the Washington Naval Treaty reconvened in London in 1930, Japanese naval officers began to chafe under the ship construction restrictions imposed upon their nation. At that time, the armed forces were unpopular with the liberal government in power. Final decision on the size of the Navy lay in the competence of the civilian government. Most career officers were hostile to the treaty; those officers, who supported the civilian government in the bitter fight that ensued concerning ratification of the 1930 London Treaty, were either forced to resign within the next few years or were placed in unimportant posts. Militarists, ascending in power, referred contemptuously to the ratification as “the May 15th Affair.”

The London Treaty carried forward the general limitations of the earlier Washington agreement and provided for further reductions of naval armament. Under terms applicable to Naval Aviation, the definition of an aircraft carrier was broadened to include ships of any tonnage designed primarily for aircraft operations. It was agreed that installation of a landing-on or flying-off platform on a warship designed and used primarily for other purposes would not make that ship an aircraft carrier. It also stipulated that no capital ship in existence on April 1, 1930 would be fitted with such a platform or deck.

Rapid expansion

The Japanese Navy expanded rapidly after 1930, at such a rate that it became necessary to conscript men. In 1931, a replenishment plan was authorised, permitting the Navy to complete construction of the Ryujo (Galloping Dragon), a small aircraft carrier of about 10,000 tons laid down in 1929. It was completed in 1933, its limited deck free of an obstructive island. Ryujo had a speed of 29 knots, carried 36 aircraft, and was armed with 12 five-inch guns. She was Japan’s fourth aircraft carrier. In June 1934, USS Ranger became the United States Navy’s fourth carrier.

In 1932, naval authorities referred a second naval replenishment plan to the Ministry of Finance for study. This called for a total expenditure of ¥460,000,000 (about $230 million), covering the construction of one aircraft carrier of 8000 tons, other capital and auxiliary ships, and the establishment of eight flying corps on land: all this to be completed by the end of 1936. This aircraft carrier was never built.

In 1934, preliminary disarmament conferences were held in London. Congress had already passed and President Roosevelt authorised an act that popularly became known as the Vinson­Trammell Act. This permitted the USA to construct naval ships to the tonnage limitations prescribed by the previous Washington and London Naval Treaties. Under this authorisation, USS Wasp (CV-7) was laid down in 1936.

Japanese militarists were not eager to continue in the disarmament pacts. Wrote U.S. Ambassador to Japan, Joseph C. Grew, “Japanese attitude toward the coming Naval Conference in 1935 London Treaty is intensely unpopular among the Japanese Naval officers high and low;” and in separate correspondence, “The situation is entirely different from that in 1930 … Under present conditions the Navy alone will have the final say [as to the size of the Imperial Japanese Navy].”

Quantitative parity

It boiled down to this: Japan wanted quantitative as well as qualitative parity in ship power, equal to the United States and Great Britain. The 5-5-3 ratio was no longer acceptable. Neither the USA nor Britain favoured such an increase in Japanese strength. Granted equality in armoured ships, Japan would be the major power in the Pacific, greater than the USA and Great Britain combined when their Fleets were divided geographically. Japan persisted. The Japanese Year Book of 1935 enumerated that country’s “official” reasoning:

1. The progress and development made recently in battleships, aeroplanes, etc., have made it extremely difficult to effectuate defence operations.

2. The remarkable increases in the air forces of the USSR and China, and the revival of the Far Eastern naval forces of the former.

3. The establishment of the naval port of Singapore by Great Britain, and the extension and strengthening of the naval port of Hawaii by the USA have had a great effect on the naval plan of operations in Far Eastern waters.

4. The birth of Manchoukuo [independence of Manchuria, 18 February 1932] has brought forth vast in Far Eastern policies. It has increased the responsibility of the Japanese Empire as the stabilizing power in the Far East.

These were political arguments the world’s two top naval powers could not buy. But Japan was adamant, refused compromise and, on December 29, 1934, gave the required two years’ formal notice that after 31 December 1936, she would no longer be bound by the terms of the Washington and London Naval Treaties. Her act of abrogation unleashed the restraints on international shipbuilding.



HIJMS Soryu, laid down in 1934 and commissioned in December 1937, displaced 19,500 tons on a 222 x 21 x 7.44 metres hull. Her four screws and 152,000 hp engines made her nearly 40 per cent faster than the similar-sized 25-knot HMAS Sydney and Melbourne.

Two more aircraft carriers were laid down in Japanese ways in 1934 and 1936, the Soryu (Blue Dragon) and Hiryu (Flying Dragon). Soryu displaced about 18,000 tons standard, had a speed of 34.5 knots, and handled 63 aircraft. Hiryu was heavier, 18,500 tons standard, and had a speed of 34.3 knots. Officially, both ships were carried on the books at 10,050 tons standard; the true tonnage was not revealed until after WW II. Both ships carried the same number of planes and had the same armament, 12 five-inch guns.



HIJMS Hiryu in 1939.

HIJMS Hiryu, sister ship to Soryu, was laid down in 1936 and commissioned in 1939. Hiryu had a port-side island, like Akagi, which meant that when operating aircraft she would be on the starboard side of a tight multi-carrier formation, with her aircraft flying right-hand circuits. The starboard-side island ships would be deployed in the port column, with their aircraft flying left-hand circuits. Hiryu was also part of the carrier group that bombed Pearl Harbour and Darwin and participated in the Indian Ocean raid. Hiryu was the only operational front line Japanese carrier left in the Battle of Midway after Kaga, Soryu and Akagi were all disabled early on 4 June 1942. In that battle, Hiryu launched two strikes, at 1050 and 1245, that severely damaged USS Yorktown (CV-5, below), leading to that carrier’s total loss. In turn, Hiryu was hit by four bombs from a strike by Yorktown‘s sister-ship Enterprise (CV-6) around 1700, which led to her scuttling early the next morning. At Midway, Hiryu carried a formidable arsenal of 21 A6M Zero fighters, 21 Aichi D3A (Val) dive bombers and 21 Nakajima B5N (Kate) torpedo bombers.



USS Yorktown (CV-5) hit amidships by a torpedo from a Hiryu-launched strike, 4 June 1942.

It was sometime between 1935 and 1937 that naval ship designers configured carriers to provide a surprising technical innovation. Akagi and Kaga underwent major modernisation at this time. The lower flight decks were suppressed, the upper flight decks were extended forward, and the eight-inch gun turrets and mountings were reduced in Akagi from ten to six, while Kaga replaced her 12 x 4.7-inch guns with 16 five-inchers. Kaga‘s unwieldy funnels were also reduced. The modernisation of Kaga, which included new machinery, added about 1½ knots to her speed, giving her 28.3, but Akagi‘s modernization cost her several knots, bringing her down to 28.

Port-side islands

But the startling innovation was the introduction of small islands on the port side of the carriers Akagi and Hiryu. The remaining carriers had islands on the starboard (standard) side—of those that had them at all. Strategists planned to use these carriers in a formation that was unique. The lead carriers in the basic formation were to be the port-islanded Hiryu and Akagi, followed by the Soryu and Kaga. This would supposedly allow for a more compact formation with nonconflicting aircraft traffic patterns. This formation was used in the Battle of Midway.

(Ed. note: This explanation remains valid only if the carriers turned together to a flying course of about 90 degrees port. See the caption to the Hiryu photo above for a better explanation.)

Japan’s next venture into aircraft carrier construction was the Shokuku (Flying Crane) and Zuikaku (Lucky Crane). These carriers were kept fairly well under wraps, insofar as specifications are concerned. They were authorised under the very ambitious Fleet Replenishment Program of 1937, the same program under which the famed super battleships Yamato and Musashi were built.

Shokaku was laid down December 12, 1937 at the Yokosuka Navy Yard, while Zuikaku was started at Kawasaki Dockyard May 25, 1938. Basically, the ships had similar specifications. They displaced 25,675 tons standard, had a designed speed of 34.2 knots, carried 16 five-inch guns in twin mounts, and could carry up to 84 aircraft, although a normal complement was 73. There were no major differences between the ships. Zuikaku, however, was fitted with a bulbous bow, the first Japanese warship so designed. Shokuku was launched June 1, 1939, and completed August 8, 1941; Zuikaku was launched November 27, 1939, and completed September 25, 1941.

Funnel modifications

Completion of both carriers was delayed when the original funnel arrangement was changed in mid-construction by the Aeronautical Headquarters. As designed, the funnels were to appear one on each side of the island bridge, fore and aft on the starboard side. This was changed by placing the two funnels immediately aft of the island.

The Japanese did not give either ship much publicity. Both ships, Zuikaku and Shokaku, were to figure prominently in most sea battles of WW II involving naval air. Their design was based on the best material gathered from experiences in Akagi, Kaga, and the Soryu types. Later Japanese carriers (i.e., multiple ship design classes) were constructed in two groups: the large to be like Taiho (with armoured flight deck) , and the medium to be repeats of the Soryu class. Zuikaku and Shokaku comprised an entire class.

Japan’s next aircraft carrier was a conversion. In 1936 the submarine depot ship Takasaki was under construction. While she was still in the ways, the decision was made to complete the ship as a carrier. Work on this project was not started until January 1940, but was completed in December that year. The carrier was renamed Zuiho (Happy Phoenix). She displaced 11,200 tons standard, sailed at 28 knots, and carried 30 aircraft. She was armed with eight five-inch guns. A sister ship, Shoho (Lucky Phoenix), converted between January 1941 and January 1942, was originally named Tsurugisaki, launched as a submarine depot ship in 1934. Zuiho and Shoho particulars were similar.

Other aircraft carriers were under construction or conversion. At least 15 more would be commissioned during the war years, produced in growing restrictions of limited materials, and, after the Battle of Midway in 1942, in desperation.

Further rapid expansion

In the five-year period preceding 7 December 1941, Japan’s military might grew stronger. In March 1936 the cabinet was dominated by men in uniform and the development of heavy industry was pushed. An extraordinarily ambitious and successful expansion of the Navy was launched in 1937, the same year hostilities broke between Japan and China. That same year, the Panay was sunk. In 1938, the National Mobilization Bill was passed. In September 1940, Germany, Italy and Japan concluded a three-power pact. November 1941, Japanese Prime minister, Gen. Hideki Tojo, stated that British and American influence must be eliminated from the Orient.



The best carrier in the world is useless without capable aircraft. The deadly Nakjima B5N (Kate) was the best of the early WW II torpedo bombers. Its 1115 hp engine gave it a speed of 200 knots and a very respectable 600-mile strike range with an 800 kg torpedo.

The Japanese Navy had been conducting intensive training of its officers and men during this period. Most of the training, including war games, was conducted in out-of-the-way gulfs and in the stormy northern reaches of the Pacific. The men were hardened by the elements and drilled continuously. To avoid antagonizing the Japanese, the U.S. Navy at the same time was instructed to hold all of its fleet problems in the less satisfactory areas west of the International Date Line.

Pearl Harbor

By 1941, Japan was determined to wage war. On November 10, VADM Chuichi Naguma, placed in charge of the initial attack, issued his first operation order on the mission. The Striking Force of Akagi, Kaga, Soryu, Hiryu, Shokaku and Zuikaku, as well as other capital ships, sortied from Kure navy base between 10 and 18 November, rendezvousing on the 22nd in Tankan Bay in the Kuriles.

ADML Yamamoto ordered the force to sortie on 26 November. On 2 December he broadcast a prearranged signal that would launch the attack on Pearl Harbor: “Niitaka Yama Nobore” (Climb Mount Niitaka). Five days later, 7 December, the Japanese Navy launched its surprise attack by aircraft, launched from carriers, at Pearl Harbour and the Philippines. The next day, the United States and Japan were officially at war.