Kaga

1. Lead

The Japanese aircraft carrier Kaga was one of the six carriers that attacked Pearl Harbor on 7 December 1941, and one of the four carriers lost by Japan at the Battle of Midway six months later. She was also one of the strangest ships in naval history: laid down as a battleship in 1920, converted into an aircraft carrier under the Washington Naval Treaty, rebuilt twice, and finally sunk on 4 June 1942 by dive bombers from the American carrier USS Enterprise, in an attack that lasted only minutes but that destroyed her and killed most of her crew. Kaga was large, slow by carrier standards, and poorly protected against fire, but she was also one of the most experienced carriers in the Imperial Japanese Navy, and her loss at Midway — with the carriers Akagi, Sōryū and Hiryū — broke the back of Japanese naval aviation and changed the course of the Pacific War.

Kaga‘s story is the story of Japanese naval aviation itself: ambitious, technically accomplished, and fatally overconfident. The ship was built from a battleship hull that was never meant to carry aircraft, and her design — with three flight decks at first, then a single full-length deck, and with her funnel bent sideways to keep smoke clear of the deck — was a series of improvisations that never quite worked.

Her aircraft were among the best in the world in 1941, and her aircrew were the most experienced in the world, but her damage control was poor, her hangars were unprotected, and her fuel and ammunition were stored in ways that made a single bomb hit fatal.

This article describes Kaga‘s background and development, her design, her variants, her operational history, her performance, her operators, her legacy and the wreck that survives.

2. Key Facts

Type	Aircraft carrier (converted battleship)
Origin	Japan
Designer	Imperial Japanese Navy; Kawasaki Shipbuilding
Builder	Kawasaki Shipbuilding, Kobe
Laid down	July 1920 (as a battleship)
Launched	November 1921
Commissioned	March 1928 (as a carrier)
Sunk	4 June 1942, Battle of Midway
Displacement	About 38,813 tons full load (after 1935 rebuild)
Length	812 ft 6 in (247.7 m)
Beam	106 ft (32.3 m)
Draught	About 31 ft (9.5 m)
Propulsion	4 steam turbines, 127,400 shp; 4 shafts
Speed	About 28.3 knots
Range	About 10,000 nautical miles at 16 knots
Crew	About 1,708 (including air group)
Aircraft	About 72–90 (1941: 18 fighters, 27 dive bombers, 27 torpedo bombers, plus spares)
Armament	10 × 8-in guns (originally); 16 × 5-in anti-aircraft guns; 22 × 25 mm anti-aircraft guns
Armour	Belt 6 in; deck 1.5 in
Most famous action	Pearl Harbor, 7 December 1941; Battle of Midway, 4 June 1942

3. Background and Development

A battleship that became a carrier

Kaga was laid down at Kawasaki Shipbuilding in Kobe in July 1920 as a battleship of the Tosa class, armed with ten 16-inch guns and designed to be one of the most powerful battleships in the world. She was launched in November 1921, but before she could be completed, the Washington Naval Treaty of 1922 limited battleship construction and forced Japan to cancel the Tosa class.

The treaty allowed Japan to convert two unfinished battleship hulls into aircraft carriers, and the Navy chose Kaga and her sister Akagi — the two hulls that were furthest advanced. The conversion was a compromise from the start: a battleship hull is narrow, heavily armoured and designed for guns, not for aircraft, and fitting a flight deck, hangars and aircraft lifts into it required ingenuity and produced a ship that was never quite satisfactory.

The three-deck experiment

When Kaga was commissioned in March 1928, she had one of the strangest flight-deck arrangements ever built: three superimposed flight decks, one above the other, so that aircraft could take off from the upper deck and from the two shorter lower decks at the same time.

The idea was to increase the rate at which aircraft could be launched, but it did not work: the lower decks were too short for the heavier aircraft that entered service in the 1930s, and the arrangement made the ship’s hangars cramped and hard to work in. Kaga also had a funnel that was bent sideways and downwards, to keep smoke clear of the flight deck, and two small funnels that could be lowered — an arrangement that was ingenious and unreliable in equal measure.

The ship’s first years were spent in trials, in training, and in the war in China, where her aircraft bombed Chinese cities and learned the techniques they would use at Pearl Harbor.

The 1935 rebuild

In 1934–1935, Kaga was taken in hand for a complete rebuild that removed the three flight decks and replaced them with a single full-length flight deck, 812 feet long, and that lengthened the hull, increased the displacement to about 38,813 tons full load, and fitted new boilers and turbines that raised her speed to about 28.3 knots.

The rebuild also enlarged the hangars, fitted a small island on the starboard side, and improved the anti-aircraft armament. The rebuilt Kaga was a far more capable ship than the original, and she was, with Akagi, the largest carrier in the Japanese Navy until the Shōkaku class entered service in 1941.

But the rebuild could not fix the ship’s fundamental weaknesses: her hangars were still unprotected, her fuel and ammunition were still stored in ways that made fire likely, and her damage control — the ability to fight a fire and keep the ship afloat — was poor by the standards of the American and British navies.

4. Design

Flight deck, hangars and island

After her 1935 rebuild, Kaga had a single full-length flight deck, 812 feet 6 inches long and 106 feet wide, with three aircraft lifts and two hangar decks below it. The hangars were large enough to carry about 72 to 90 aircraft, depending on the type, and the ship’s air group in December 1941 consisted of 18 Mitsubishi A6M Zero fighters, 27 Aichi D3A dive bombers and 27 Nakajima B5N torpedo bombers, plus spares — a total of about 72 operational aircraft and about 18 in reserve.

The island, on the starboard side, was small and contained the bridge, the flight-control station and the funnel, which was bent downwards and to the side to keep smoke clear of the deck. The arrangement worked, but it was a compromise: the island was too small for the ship’s size, and the funnel’s bend reduced the boilers’ efficiency and made the ship’s smoke a problem in certain winds.

Armament and protection

Kaga‘s armament reflected her battleship origins and her role as a carrier. She originally carried ten 8-inch guns in casemates, a legacy of the days when carriers were expected to defend themselves against cruisers with guns, but by 1941 most of those guns had been removed and the ship relied on sixteen 5-inch anti-aircraft guns and twenty-two 25 mm anti-aircraft guns for defence.

The 25 mm gun was a poor weapon — short-ranged, slow-firing, and mounted in single and triple mounts that were hard to aim — and Kaga‘s anti-aircraft defence was, by American standards, weak. Her armour was also weak: a belt of 6 inches, a deck of only 1.5 inches, and no armoured flight deck.

A bomb that hit the flight deck could penetrate into the hangars, where aircraft, fuel and bombs were stored together, and start a fire that the ship’s damage-control parties could not fight. That weakness, more than any other, killed Kaga at Midway.

Machinery, speed and crew

Kaga was powered by four steam turbines, of 127,400 shaft horsepower in total, driving four shafts, and she could make about 28.3 knots — fast enough to keep up with the fleet, but slower than the American carriers Enterprise and Yorktown, which could make 32 knots or more.

Her range was about 10,000 nautical miles at 16 knots, which gave her the reach to operate from Japan to Hawaii and back. Her crew was about 1,708 men, including the air group — pilots, mechanics, armourers and flight-deck crews — who lived in conditions that were cramped but, by Japanese standards, comfortable.

The ship’s air group was the heart of her fighting power, and its pilots, in 1941, were the most experienced carrier pilots in the world, with hundreds of hours of flying time and combat experience in China. That experience was Kaga‘s greatest strength, and its loss at Midway was Japan’s greatest loss.

5. Variants

Form	Years	Key features
Kaga as battleship (uncompleted)	1920–1922	Tosa-class battleship, ten 16-in guns; cancelled by Washington Treaty
Kaga as carrier, three decks	1928–1934	Three superimposed flight decks; bent funnel; about 60 aircraft
Kaga as carrier, rebuilt	1935–1942	Single full-length flight deck; 812 ft; about 72–90 aircraft; 28.3 knots
Akagi (sister, for comparison)	1927–1942	Larger, three decks then rebuilt; sunk at Midway with Kaga

One ship, three forms

Kaga was, in effect, three different ships: a battleship that was never completed, a carrier with three flight decks that did not work, and a rebuilt carrier with a single flight deck that did. The three forms are a record of the Imperial Japanese Navy’s learning curve in carrier aviation — from the battleship navy that built Kaga as a gun ship, through the experimental navy that tried three decks, to the carrier navy that rebuilt her into a ship that could fight at Pearl Harbor and Midway.

The rebuilt Kaga was the ship that mattered, and it was the ship that fought the war. Her sister Akagi, built from a battlecruiser hull, was larger and faster, but she shared Kaga‘s weaknesses — unprotected hangars, poor damage control, and a weak anti-aircraft battery — and she shared Kaga‘s fate at Midway, sunk on the same day by the same American dive bombers.

The air group

Kaga‘s air group changed over her career, as new aircraft entered service. In the war in China, she flew Aichi D1A biplane dive bombers and Nakajima A4N fighters; by 1941, she flew the Mitsubishi A6M Zero fighter, the Aichi D3A dive bomber and the Nakajima B5N torpedo bomber — the three aircraft that made Japanese naval aviation the best in the world in 1941.

The Zero was faster and more manoeuvrable than any American fighter; the D3A was accurate and reliable; and the B5N was the best torpedo bomber in the world. The air group’s pilots were the most experienced in the world, and their skill, more than the ship’s design, made Kaga a formidable weapon.

But the air group’s strength was also its weakness: Japan could not replace its experienced pilots, and when they were lost — at Midway, in the Solomons, and in the Marianas — they were gone for good.

No post-war career

Kaga had no post-war career, and no sister survived her. She was sunk at Midway on 4 June 1942, and her sister Akagi was sunk on the same day. The Shōkaku class, which followed them, was built as a carrier from the start and was a better ship, but it too was lost in the war. The Japanese carrier force that Kaga had been part of — the Kido Butai, the Mobile Force — was destroyed at Midway, and Japan never rebuilt it. Kaga‘s story is therefore a story of a ship that fought only one war, and that died in the battle that decided it.

The absence of a post-war career is itself a measure of Midway’s decisiveness. Japan built new carriers after 1942 — the Taiho, the Shinano, and the Unryu class — but it could not replace the pilots and mechanics lost at Midway, and the new carriers, when they fought, were crewed by inexperienced air groups that could not match the Americans. Kaga’s death at Midway was therefore not merely the loss of a ship, but the loss of the human capital that had made the ship effective.

6. Operational History

The war in China and Pearl Harbor

Kaga fought in the war in China from 1937, where her aircraft bombed Shanghai, Nanking and other Chinese cities, and where her pilots learned the dive-bombing and torpedo techniques they would use at Pearl Harbor. On 7 December 1941, Kaga was one of the six carriers of the Kido Butai that attacked Pearl Harbor, under Vice Admiral Chūichi Nagumo.

Her aircraft — 27 torpedo bombers and 18 dive bombers in the first wave, and more in the second — attacked the American battleships, sinking or damaging eight of them, and her pilots claimed a large share of the damage. Kaga herself was not attacked, and she returned to Japan with the rest of the force, having taken part in the most successful carrier operation in history.

The attack on Pearl Harbor made Kaga famous in Japan, and it made her a symbol of Japanese naval power.

The Indian Ocean and the Coral Sea

The Indian Ocean raid

In April 1942, Kaga took part in the Indian Ocean raid, in which the Kido Butai sailed into the Indian Ocean, sank the British aircraft carrier HMS Hermes, two British cruisers and several other ships, and bombed Colombo and Trincomalee in Ceylon.

The raid was a triumph for Japanese naval aviation, and it showed that the Kido Butai could operate far from home and defeat any force it met. Kaga‘s aircraft took part in the sinking of Hermes and in the bombing of the British bases, and the ship returned to Japan in triumph, having fought in every major operation of the war’s first five months without being damaged.

The raid was the high point of Kaga‘s career, and it was also the last operation she would fight before Midway.

The road to Midway

Kaga did not take part in the Battle of the Coral Sea in May 1942, because she was in Japan for repairs and for the embarkation of a new air group. The Coral Sea was the first carrier-versus-carrier battle in history, and it cost Japan the carrier Shōhō and damaged Shōkaku, but it also cost the United States the carrier Lexington.

The Japanese high command, believing that the American carrier force had been weakened, planned Operation MI — the invasion of Midway Island — and sent the Kido Butai, with Kaga, Akagi, Sōryū and Hiryū, to cover the invasion. The American Navy, which had broken the Japanese naval code, knew the plan and laid an ambush: three American carriers — Enterprise, Hornet and Yorktown — waited northeast of Midway, ready to strike. Kaga sailed for Midway on 26 May 1942, in the confident belief that the battle would be a Japanese victory.

The Battle of Midway

On the morning of 4 June 1942, Kaga‘s aircraft took part in the bombing of Midway Island, and then, while the ship was rearming her aircraft for a second strike — with bombs and torpedoes stacked on the hangar decks and fuel lines open — American dive bombers from USS Enterprise arrived overhead.

At about 10:22, three squadrons of American SBD Dauntless dive bombers, led by Lieutenant Commander Wade McClusky, attacked Kaga, Akagi and Sōryū simultaneously, catching the Japanese carriers with their decks full of armed and fuelled aircraft. Kaga was hit by four 1,000-pound bombs, one of which struck the flight deck near the island and penetrated into the hangar, where it set off a chain of explosions among the armed aircraft, the fuel and the bombs.

The ship was engulfed in fire within minutes, her damage-control parties were killed or driven off by the flames, and the fire spread unchecked through the hangars and up to the flight deck. Captain Jisaku Okada and most of the ship’s officers were killed, and the crew abandoned ship in the afternoon. Kaga sank at about 19:25 on 4 June, with the loss of about 811 of her 1,708 crew.

The sinking, with the loss of Akagi, Sōryū and Hiryū on the same day, broke the Kido Butai and changed the course of the war.

The wreck

Kaga‘s wreck was found in October 2019 by the research vessel Petrel, at a depth of about 5,400 metres (about 17,700 feet) northwest of Midway, lying upright on the seabed with her flight deck largely intact. The discovery, by the team led by Robert Ballard’s collaborators and the Petrel expedition, confirmed the ship’s identity and gave historians their first look at the ship since she sank. The wreck is a war grave, and it is protected as such: the men who died aboard Kaga are still there, and the ship is left undisturbed. The discovery was reported around the world, and it brought Kaga‘s story back into the public eye, seventy-seven years after she sank.

The discovery of the wreck also settled a long-standing question about Kaga’s final hours. The wreck lies upright, with her flight deck largely intact, which is consistent with the accounts of survivors, who described the ship sinking slowly, after the fires had burned themselves out, rather than breaking up on the surface. The images from the Petrel expedition show a ship that is recognisably Kaga, and they have allowed historians to confirm details of her construction that had previously been known only from plans.

7. Performance and Specifications

Specifications in full

The figures in the table below are Kaga‘s figures after her 1935 rebuild, taken from Japanese naval records and from post-war studies. Displacement, speed and aircraft numbers varied over her career, because the air group changed as new aircraft entered service and because the ship’s fittings were altered in successive refits.

The aircraft figure of about 72 to 90 is a range, not a single number: in December 1941, Kaga carried 72 operational aircraft plus spares, and her maximum capacity was about 90. The armour figures are the design figures: the belt was 6 inches thick, the deck 1.5 inches, and the flight deck was unarmoured — a fact that mattered fatally at Midway, when a single bomb penetrated into the hangar and set off the explosions that destroyed the ship.

Specification	Kaga (after 1935 rebuild)
Displacement (full load)	About 38,813 tons
Length	812 ft 6 in (247.7 m)
Beam	106 ft (32.3 m)
Speed	About 28.3 knots
Range	About 10,000 nautical miles at 16 knots
Aircraft	About 72–90
Main guns	10 × 8-in (originally, reduced by 1941)
Anti-aircraft guns	16 × 5-in; 22 × 25 mm
Belt armour	6 in (152 mm)
Deck armour	1.5 in (38 mm)
Flight deck	Unarmoured
Crew	About 1,708 (including air group)

Comparison with other carriers

Compared with the American carrier USS Enterprise, Kaga was larger — about 38,813 tons full load against Enterprise‘s about 25,500 tons — but slower, at 28.3 knots against Enterprise‘s 32.5 knots, and more lightly protected, with an unarmoured flight deck against Enterprise‘s wooden deck over a steel hangar deck and with a far weaker anti-aircraft battery.

Compared with her sister Akagi, Kaga was smaller and slower, but she carried a similar air group and she shared Akagi‘s weaknesses. Compared with the British carrier HMS Illustrious, Kaga carried more aircraft but was far less well protected, with an unarmoured flight deck against Illustrious‘s 3-inch armoured flight deck.

In 1941, Kaga‘s strength was not her design but her air group: her pilots were the best in the world, and her aircraft were the best in the world, and for six months those two facts were enough. At Midway, they were not enough, and the ship’s design — unprotected hangars, poor damage control, weak anti-aircraft guns — killed her.

8. Operators

The Imperial Japanese Navy

Kaga was built for, and served only in, the Imperial Japanese Navy, which operated her from her commissioning in March 1928 until her sinking in June 1942. In Japanese hands she served as a fleet carrier in the First Carrier Division, with Akagi, and she was the flagship of the Kido Butai at times and the ship that carried the largest air group in the force.

Her crew were Japanese, her pilots were Japanese, and her story is a Japanese story: the story of a navy that built the best carrier aviation in the world and then lost it, in a single morning, at Midway. The ship’s officers included some of the most famous men in the Japanese Navy — Captain Jisaku Okada, who died with her at Midway, and the air-group commanders who led her aircraft at Pearl Harbor and in the Indian Ocean.

No foreign operators

No other navy ever operated Kaga, and no ship of her design was ever built by another navy. The class consisted of a single ship — Kaga herself — and her sister Akagi was built from a different hull, a battlecruiser, to a different design.

The ship’s story is therefore an entirely Japanese story, from the battleship hull laid down at Kawasaki in 1920 to the wreck found northwest of Midway in 2019. The name Kaga — after the old Kaga Province — was later given to a Japanese helicopter destroyer, JS Kaga (DDH-184), commissioned in 2017 and converted into a light aircraft carrier in the 2020s, a deliberate echo of the name and of the ship’s place in Japanese naval history.

The ship’s Japanese-only service also reflects the closed character of the Imperial Japanese Navy, which built its carriers for its own doctrine and shared little with other navies. Kaga’s design — a battleship hull converted to a carrier, with three decks and then one — was a Japanese solution to a Japanese problem, and no other navy attempted it. The ship’s story is therefore a purely Japanese story, and its wreck, found by an American expedition, is a shared memorial to a battle that both navies remember.

9. Legacy and Influence

The turning point of the Pacific War

Kaga‘s legacy is the Battle of Midway itself. Her sinking, with Akagi, Sōryū and Hiryū on 4 June 1942, broke the Kido Butai and ended Japan’s ability to fight a carrier war on equal terms with the United States. Japan lost four carriers and, more importantly, lost the experienced pilots and mechanics who had made those carriers effective, and it never replaced them.

The battle is now regarded as the turning point of the Pacific War, and Kaga‘s loss is central to that story: she was the largest carrier in the force, she carried the largest air group, and her destruction in a few minutes, by a handful of dive bombers, showed that the carrier war would be decided not by the size of a ship but by the skill of its pilots, the quality of its damage control, and the luck of a single morning.

Lessons in carrier design

Kaga also left a lesson in carrier design that every navy learned from her loss. Her unprotected hangars, her poor damage control, and her weak anti-aircraft battery were the weaknesses that killed her, and the carriers built after Midway — American, British and Japanese alike — were designed with those weaknesses in mind: armoured flight decks, protected hangars, better damage control, and heavier anti-aircraft batteries.

The American Essex class, which entered service in 1943, carried more aircraft than Kaga, was faster, and was far better protected, and it was the ship that won the carrier war. Kaga‘s name, given to a modern Japanese carrier, is a reminder that the ship’s story is still remembered in Japan, and that the lessons of Midway are still taught to young officers in every navy in the world.

10. Surviving Examples

The wreck northwest of Midway

No part of Kaga survives above water. The ship sank on 4 June 1942, and her wreck lay undiscovered for seventy-seven years, until the research vessel Petrel found it in October 2019 at a depth of about 5,400 metres northwest of Midway.

The wreck lies upright on the seabed, with her flight deck largely intact, and the images from the Petrel expedition show a ship that is recognisably Kaga — her island, her funnel, and her flight deck all visible in the deep water. The wreck is a war grave, and it is protected as such: the men who died aboard Kaga are still there, and the ship is left undisturbed.

The discovery was reported around the world, and it brought Kaga‘s story back into the public eye, seventy-seven years after she sank.

Memorials and the name

Kaga is remembered in Japan at the naval memorials at Kure and Yokosuka, and in the United States at the Midway memorials and at the museums that tell the story of the Pacific War. Her name lives on in the modern Japanese carrier JS Kaga (DDH-184), commissioned in 2017, which carries the name deliberately, as a link to the ship that fought at Pearl Harbor and died at Midway.

For anyone who wants to understand the Battle of Midway, the story of Kaga — a battleship that became a carrier, a carrier that attacked Pearl Harbor, and a ship that died in a few minutes on a June morning — is the best introduction there is, because it is the story of Japanese naval aviation itself, from its triumph to its destruction.

Frequently Asked Questions

What is Kaga?
Kaga was a Japanese aircraft carrier of the Second World War, built as a battleship, converted to a carrier, and sunk at the Battle of Midway on 4 June 1942. She was one of the six carriers that attacked Pearl Harbor.

Was Kaga originally a battleship?
Yes. Kaga was laid down in July 1920 as a Tosa-class battleship with ten 16-inch guns. The Washington Naval Treaty of 1922 cancelled the class, and Kaga was converted into an aircraft carrier instead.

How many aircraft did Kaga carry?
About 72 operational aircraft in December 1941 — 18 Zero fighters, 27 D3A dive bombers and 27 B5N torpedo bombers — plus spares, for a maximum capacity of about 90.

How was Kaga sunk at Midway?
On 4 June 1942, dive bombers from USS Enterprise hit Kaga with four 1,000-pound bombs while her hangars were full of armed and fuelled aircraft. Fires and explosions spread unchecked, and she sank that evening with the loss of about 811 men.

Where is Kaga’s wreck?
Kaga‘s wreck was found in October 2019 by the research vessel Petrel, at a depth of about 5,400 metres northwest of Midway, lying upright on the seabed. It is a protected war grave.

Is there a modern ship named Kaga?
Yes. JS Kaga (DDH-184), a Japanese helicopter destroyer commissioned in 2017, was named after the carrier and has been converted into a light aircraft carrier in the 2020s.

Related articles

• 44M Tas Tank
• A-20 Havoc
• Balao-class Submarine

Sources

1. Wikipedia, “Japanese aircraft carrier Kaga” — battleship origins, three decks, 1935 rebuild, Pearl Harbor, Midway, wreck found 2019.
2. Jonathan Parshall and Anthony Tully, Shattered Sword: The Untold Story of the Battle of Midway (Potomac Books, 2005) — Midway, the 10:22 attack, damage control and losses.
3. Mark Peattie, Sunburst: The Rise of Japanese Naval Air Power, 1909–1941 (Naval Institute Press, 2001) — carrier development and the Kido Butai.
4. Naval History and Heritage Command, Battle of Midway histories — Enterprise dive bombers and the sinking of Kaga.
5. Hansgeorg Jentschura, Dieter Jung and Peter Mickel, Warships of the Imperial Japanese Navy, 1869–1945 (Naval Institute Press, 1977) — specifications and rebuild.
6. Robert Ballard and the Petrel expedition reports, 2019 — discovery of Kaga‘s wreck northwest of Midway.