Yokosuka D4Y Suisei (Judy) — History, Specs & Stories

Yokosuka D4Y Suisei Judy carrier dive bomber launching in 1944
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Yokosuka D4Y Suisei
“Judy”

The fastest carrier dive bomber of the Pacific War — a sleek, inline-engined “Comet” built for speed, undone by its temperamental engine, and expended at the end in kamikaze fire.

579 km/hTop speed · D4Y2 variant
~2,038Aircraft built · 1940–1945
560 kgBomb load · one 500 kg bomb internally
1940First flight · in service from 1942
Photo: Imperial Japanese Navy · Public domain
RoleCarrier dive bomber & reconnaissanceEraWorld War IIMotorAichi Atsuta inline / Mitsubishi Kinsei radialOriginJapan · Yokosuka Naval Air ArsenalStatusRetired · not flyableCan you still fly a D4Y today?
Het verhaal

The Yokosuka D4Y Suisei: built for speed, betrayed by its engine

By the late 1930s the Imperial Japanese Navy wanted a carrier dive bomber that could outrun the fighters sent to stop it. The fixed-gear Aichi D3A “Val” then in service was rugged but slow, and the Navy’s planners looked to Germany for a faster shape. In 1938 Japan bought examples of the Heinkel He 118 dive bomber; the sole imported machine was destroyed in testing, but its clean, liquid-cooled lines pointed the way. The Navy’s own Yokosuka arsenal (the Kugisho) was tasked with a sleek, fast successor, and the result — first flown in December 1940 — was named Suisei, “Comet.” The Allies would call it “Judy.”

What made the D4Y unusual was its engine. Almost every Japanese naval aircraft used an air-cooled radial; the Suisei instead carried an Aichi Atsuta, a licence-built version of the German Daimler-Benz DB 601 inverted-V12. The narrow inline let designers wrap a slender, low-drag fuselage around it, and the D4Y became the fastest carrier dive bomber of the war, touching around 580 km/h. It was so fast and long-legged that its combat debut was not as a bomber at all: two D4Y1-C reconnaissance machines flew from the carrier Sōryū at Midway in June 1942 — and went down with her when she was sunk.

The speed came at a price. The Atsuta was notoriously unreliable: hard to build, hard to maintain, and often unserviceable in the field, where Japan lacked the precision industry the German engine demanded. Early D4Y1s also suffered wing flutter in the dive, delaying the true dive-bomber version until 1943. To escape the engine altogether, the later D4Y3 En D4Y4 abandoned the inline for a conventional Mitsubishi Kinsei radial — less elegant, blunter in the nose, but dependable.

By the time the Suisei was available in numbers, the war had turned. At the Battle of the Philippine Sea in June 1944, scores of D4Ys were thrown against the US fleet and cut down by radar-directed fighters and proximity-fused flak in the rout later nicknamed the “Marianas Turkey Shoot.” Yet the type could still bite: in October 1944 a single D4Y put one bomb through the deck of the light carrier USS Princeton and doomed her. As trained crews and fuel ran out, surviving Suiseis were turned into kamikaze aircraft. The very last Japanese air sortie of the war, on 15 August 1945, was a group of D4Ys led by Vice Admiral Matome Ugaki into the sea off Okinawa.

The fastest dive bomber Japan ever flew — and the one its own engine kept grounding.The Comet’s paradox — speed no rival could match, reliability it never had
01The Yokosuka D4Y’s German bloodline: how the Heinkel He 118 shaped Japan’s Comet

In 1938 the Imperial Japanese Navy purchased the Heinkel He 118, a liquid-cooled monoplane dive bomber that had lost Germany’s own competition to the Ju 87 Stuka. The single imported airframe was wrecked in trials, but the Navy had already seen what it wanted: a clean, fast, inverted-V12 layout utterly unlike the fat radials of the D3A. The Yokosuka arsenal used that inspiration — together with a licence for the Daimler-Benz DB 601 engine — to design a slender all-new aircraft. The exact degree of Heinkel influence is debated, but the DB 601 licence and the He 118’s aerodynamic thinking are the reasons the Suisei looked and flew so differently from every other Japanese carrier bomber.

Design & Engineering

What makes the D4Y Suisei special

01

A liquid-cooled inline in a sea of radials

Alone among Japan’s carrier bombers, the D4Y was built around an Aichi Atsuta — a licence-built Daimler-Benz DB 601 inverted-V12. The slim inline let designers draw a low-drag fuselage barely wider than the pilot, and an internal bomb bay kept the belly clean. The payoff was speed: roughly 580 km/h, faster than the Allied dive bombers it faced and quick enough to be used as a fleet scout.

02

The engine that broke the Comet

The Atsuta demanded German-grade precision manufacturing Japan could not sustain in wartime. Engines arrived late, ran rough and were often unserviceable in the field. Whole squadrons sat grounded for want of working powerplants. The fix was radical: the D4Y3 En D4Y4 threw out the inline entirely for a dependable Mitsubishi Kinsei radial — blunter and slightly slower, but reliable.

03

Fast and long-legged — and unarmored

To stay light and fast the Suisei carried no armor and no self-sealing fuel tanks. Speed was its defence. That worked early on, but by 1944 — against radar-directed Hellcats and proximity-fused flak — an unprotected, lightly armed dive bomber burned easily. The same fragility that made it fast made it desperately vulnerable in a defended sky.

02The Yokosuka D4Y’s engine trouble: why Japan abandoned the inline Atsuta

The Aichi Atsuta was a fine engine on paper — a licensed DB 601 giving 1,200 hp in the D4Y1 and around 1,400 hp in the D4Y2. In practice it was a maintenance nightmare. The DB 601 relied on close machining tolerances and quality alloys that wartime Japanese industry, starved of materials and skilled labour, struggled to reproduce. Serviceability rates were poor and spare engines scarce. Rather than keep fighting the inline, Yokosuka re-engined the aircraft with the air-cooled Mitsubishi Kinsei 62 radial (~1,560 hp) to create the D4Y3. The nose grew fatter and top speed dipped slightly, but the radial could actually be kept running — the difference between an aircraft on the flight deck and one in the hangar.

03The Yokosuka D4Y2-S night fighter: the Comet sent up against the B-29

As American B-29s began night raids on Japan, a handful of Suiseis were converted into improvised night fighters as the D4Y2-S. The bomb bay and rear gun made way for an obliquely mounted 20 mm cannon — a “Schräge Musik”-style upward-firing weapon meant to be walked up into a bomber’s belly from below. Without airborne radar and short on high-altitude performance, the type was never an effective interceptor, but it is a telling snapshot of a Navy improvising with whatever airframes it had left.

Technical Data

Yokosuka D4Y Suisei: full specifications

Airframe & Performance

Bemanning
2 (pilot & observer/gunner)
Lengte
10.22 m
Spanwijdte
11.50 m
Hoogte
3.30 m
Max takeoff weight
~4,657 kg
Max speed
579 km/h (D4Y2) · 552 km/h (D4Y1)
Kruissnelheid
~425 km/h
Serviceplafond
~10,700 m
Bereik
~1,465 km · further as a scout with drop tanks
Bomb load
560 kg (one 500 kg bomb internally); up to ~800 kg

Propulsion, Armament & Production

Engine (D4Y1/D4Y2)
Aichi Atsuta (licensed DB 601) inverted-V12
Power
~1,200 hp (Atsuta 12) · ~1,400 hp (Atsuta 32)
Engine (D4Y3/D4Y4)
Mitsubishi Kinsei 62 radial · ~1,560 hp
Bewapening
2 × fixed 7.7 mm + 1 × flexible rear 7.92/13 mm
First flight
December 1940
Built
~2,038 (1940–1945)
Unit cost
No reliable public figure
Cost per flight hour
No reliable figure exists
04The Yokosuka D4Y’s cost: why no reliable price exists

The D4Y was a wartime state product of the Imperial Japanese Navy, built by the Yokosuka arsenal and Aichi under a command economy, never sold on any open market. No credible flyaway unit price, and certainly no cost-per-flight-hour figure, survives in the public record — the accounting simply was not kept or published in those terms, and much of Japan’s wartime documentation was destroyed in 1945. Any precise dollar or yen figure attached to a Suisei today should be treated as guesswork. What can be said is qualitative: the inline Atsuta made early Suiseis expensive and labour-intensive to keep flying, which is a large part of why Japan switched later airframes to the cheaper, simpler radial.

Timeline

From carrier scout to kamikaze: the D4Y Suisei’s war

1938

A German blueprint

Japan imports the Heinkel He 118 and a Daimler-Benz DB 601 engine licence, seeding the design of a fast, inline-engined dive bomber.

1940

First flight

The prototype Suisei flies in December 1940 — a slender machine unlike any other Japanese carrier bomber.

1942

Debut at Midway — as a scout

Two D4Y1-C reconnaissance aircraft operate from the carrier Sōryū at Midway and are lost when she is sunk in June.

1943

Dive bomber at last

After wing-flutter fixes, the D4Y1 enters service as a full dive bomber; the radial-engined D4Y3 follows to escape the troublesome Atsuta.

Jun 1944

The Philippine Sea

Massed D4Ys are flung at the US fleet and slaughtered by radar-directed fighters and proximity flak in the “Marianas Turkey Shoot.”

Oct 1944

USS Princeton

A single D4Y plants one bomb through the flight deck of the light carrier USS Princeton, triggering fires that sink her.

Mar 1945

USS Franklin crippled

Off Japan, a lone dive bomber — commonly attributed to a D4Y — puts two bombs into USS Franklin, causing one of the US Navy’s worst carrier disasters.

15 Aug 1945

The last sortie

Vice Admiral Matome Ugaki leads a final flight of D4Ys on a kamikaze mission off Okinawa — the last Japanese air attack of the war.

Stories & Eyewitnesses

From the cockpit: twelve D4Y Suisei stories

Origins

A comet born from a German loser

The Heinkel He 118 lost Germany’s dive-bomber contest — then shaped Japan’s fastest carrier bomber.

Read the full story
The He 118 was beaten by the Ju 87 Stuka in Germany, but its clean liquid-cooled lines impressed the Imperial Japanese Navy, which bought one in 1938. The airframe was wrecked in testing, yet the idea survived: the Yokosuka arsenal used a DB 601 engine licence and the He 118’s aerodynamic thinking to build an all-new aircraft. The Suisei that emerged looked nothing like any other Japanese carrier bomber — slim, fast and inline-powered.
Midway · 1942

Two Comets go down with Sōryū

The D4Y’s first combat use was as a scout — and both machines were lost with their carrier.

Read the full story
So fast and long-ranged was the Suisei that the Navy first used it not as a bomber but as a fleet reconnaissance aircraft. Two D4Y1-C scouts were aboard the carrier Sōryū at Midway in June 1942. When American dive bombers turned Sōryū into a blazing wreck, the two Comets went down with her — an inglorious combat debut for one of the war’s most advanced carrier aircraft.
Design

Why the bomber flew as a spy

Wing flutter in the dive kept the D4Y out of its intended role for over a year.

Read the full story
The Suisei was designed as a dive bomber, but early airframes suffered dangerous wing flutter when they pulled out of a steep dive. While engineers chased the problem, the fast, clean aircraft was pressed into service as a reconnaissance platform instead. Only in 1943, after structural fixes, did the D4Y finally enter service in the role it had been built for — by which time the tide of the Pacific War was already turning against Japan.
The engine

The Atsuta that grounded squadrons

A German engine Japan could not reliably build kept the fastest dive bomber in the hangar.

Read the full story
The Aichi Atsuta was a licence-built Daimler-Benz DB 601 — superb in theory, punishing in practice. It demanded machining tolerances and alloys that wartime Japanese industry could rarely meet, so engines arrived late, ran rough and broke often. Serviceability was chronically poor and spares scarce. The Suisei could outrun almost anything when it flew; the trouble was keeping enough of them flyable at once.
The fix

Radial rescue: the D4Y3

Japan gave up on the elegant inline and bolted on a dependable radial instead.

Read the full story
To escape the Atsuta, Yokosuka re-engined the aircraft with the air-cooled Mitsubishi Kinsei 62 radial, creating the D4Y3. The nose grew blunter and top speed slipped a little, but the radial could actually be kept running in the field. It was a very Japanese wartime compromise: trade a sliver of the Comet’s famous speed for the simple ability to get it off the deck when it was needed.
Philippine Sea · 1944

Into the Turkey Shoot

Scores of Suiseis were thrown at the US fleet — and cut down almost to a machine.

Read the full story
At the Battle of the Philippine Sea in June 1944, more than a hundred D4Y dive bombers and their crews were committed against Admiral Spruance’s carriers. Radar-directed Hellcats and proximity-fused anti-aircraft fire tore into the incoming waves before most could reach their targets. American aircrew called it the “Marianas Turkey Shoot.” The Suisei was fast, but by 1944 speed alone could not carry an unarmored aircraft through a modern air-defence screen.
USS Princeton · 1944

One bomb, one carrier

A single D4Y put one bomb through Princeton’s deck — and that was enough.

Read the full story
On 24 October 1944, during the Battle of Leyte Gulf, a lone D4Y slipped through and dropped a single bomb onto the light carrier USS Princeton. It punched through the flight deck and set off fires that spread to fuel and munitions; despite hours of firefighting, Princeton could not be saved and was scuttled. It was a stark demonstration that even a fading force could still land a lethal blow with one well-aimed aircraft.
USS Franklin · 1945

The carrier that would not die

A lone dive bomber — commonly attributed to a D4Y — nearly destroyed one of America’s biggest carriers.

Read the full story
On 19 March 1945, off the Japanese coast, a single aircraft dived out of the cloud and put two bombs into the fleet carrier USS Franklin. The explosions and fires killed hundreds and left the ship a burning ruin; she survived only through extraordinary damage control. The attacking aircraft is most often identified as a D4Y, though the attribution is contested in some accounts. Either way, Franklin became one of the worst — and most heroic — carrier survival stories of the war.
Night defence

The D4Y2-S against the B-29

A dive bomber pressed into service as a makeshift night fighter over Japan.

Read the full story
As B-29s burned Japan’s cities by night, the Navy converted a few Suiseis into D4Y2-S night fighters, fitting an obliquely mounted 20 mm cannon to fire upward into a bomber’s belly. Without radar and short on high-altitude climb, they were never effective interceptors. But they show how thoroughly Japan was improvising by 1945 — sending a carrier dive bomber up into the dark to hunt the largest bombers in the world.
Design philosophy

Speed instead of armor

The Suisei carried no protection at all — a gamble that stopped paying off.

Read the full story
Like most early-war Japanese aircraft, the D4Y traded protection for performance: no armor plate, no self-sealing fuel tanks. When the enemy’s fighters were slower and its flak less accurate, raw speed was a workable defence. But against 1944-era radar direction, faster fighters and proximity fuses, an unprotected airframe simply caught fire and fell. The very lightness that made the Comet fast is what made it so lethal to fly in a defended sky.
Kamikaze

The Comet as a weapon

As crews and fuel ran out, surviving Suiseis were turned into guided bombs.

Read the full story
By late 1944 Japan lacked the trained aircrew and fuel to fight conventionally, and many surviving D4Ys were assigned to special-attack — kamikaze — units. A fast, long-ranged aircraft that could carry a heavy bomb made a natural, terrible choice. The dedicated D4Y4 single-seat variant was built for exactly this. It was an ignoble end for an aircraft conceived as the sharpest carrier bomber in the fleet.
15 August 1945

Ugaki’s last flight

The war’s final Japanese air sortie was flown by Suiseis into the sea off Okinawa.

Read the full story
Hours after Emperor Hirohito announced Japan’s surrender on 15 August 1945, Vice Admiral Matome Ugaki stripped off his rank insignia, climbed into a D4Y and led a small flight of Suiseis on a final kamikaze mission toward Okinawa. None returned, and no confirmed hits resulted. It was the last Japanese air attack of the Second World War — and the Suisei, first blooded at Midway, was there at the very end.
Gallery

The D4Y Suisei in pictures

A D4Y1 Suisei launches from the carrier Juny during the Battle of the Philippine Sea, June 1944.
A D4Y1 Suisei launches from the carrier Jun’yō during the Battle of the Philippine Sea, June 1944.Photo: Imperial Japanese Navy · Public domain
A wartime D4Y1 Suisei lifting off the fastest carrier dive bomber Japan flew.
A wartime D4Y1 Suisei lifting off — the fastest carrier dive bomber Japan flew.Photo: Imperial Japanese Navy · Public domain
A D4Y3 Suisei pulling up in flight, showing the clean lines of the Comet.
A D4Y3 Suisei pulling up in flight, showing the clean lines of the “Comet.”Photo: Public domain
A D4Y3 Suisei airframe photographed on the ground after capture.
A D4Y3 Suisei airframe photographed on the ground after capture.Photo: Public domain
The sole surviving D4Y airframe, preserved at the Yshkan museum in Tokyo.
The sole surviving D4Y airframe, preserved at the Yūshūkan museum in Tokyo.Photo: Michael Voss · CC BY-SA 4.0
A restored D4Y3 Suisei at the Planes of Fame Air Museum, California.
A restored D4Y3 Suisei at the Planes of Fame Air Museum, California.Photo: Gabloc · CC BY-SA 4.0
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The Blackbird in motion

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Operations

Where the D4Y Suisei fought

Combat Record

The D4Y Suisei: the record that defines it

The Suisei’s war is a story of speed against overwhelming odds. It was the fastest carrier dive bomber of the conflict, yet it arrived in numbers just as Japanese naval air power collapsed. Its greatest blows were struck not in massed raids but by lone aircraft that slipped through — and, at the very end, by aircraft flown deliberately into their targets.

579 km/hFastest carrier dive bomber of the war
1 carrier sunkUSS Princeton — one bomb from a single D4Y (1944)
Last sortieLed the final Japanese air attack, 15 Aug 1945

Compare the combat record of every military aircraft. Figures as of August 2026.

Questions & Answers

Everything people ask about the D4Y Suisei

Can I fly in a Yokosuka D4Y Suisei?
No — there are no flyable D4Y Suisei anywhere. Only one substantially complete airframe survives, on static display at the Yūshūkan museum in Tokyo, with restored examples elsewhere; none are airworthy. You can, however, fly in several genuine ex-military jets today — see migflug.com/flights-prices/.
How fast was the D4Y Suisei?
About 579 km/h (360 mph) in the D4Y2, and around 552 km/h in the earlier D4Y1. That made it the fastest carrier dive bomber of the Second World War — fast enough that its first combat role was high-speed reconnaissance rather than bombing.
Why is the D4Y called “Judy”?
“Judy” was the Allied reporting name. During the Pacific War the Allies assigned short code names to Japanese aircraft — generally female names for bombers and male names for fighters — because the Japanese designations were hard to use in the field. The aircraft’s own name, Suisei, means “Comet.”
What engine did the D4Y use?
Early D4Y1 and D4Y2 versions used the Aichi Atsuta, a licence-built Daimler-Benz DB 601 liquid-cooled inverted-V12 — unusual for a Japanese carrier aircraft. It gave great speed but was unreliable and hard to maintain, so the later D4Y3 and D4Y4 switched to a dependable Mitsubishi Kinsei radial.
Did a D4Y ever sink an American aircraft carrier?
Yes. On 24 October 1944 a single D4Y put one bomb through the light carrier USS Princeton, starting fires that led to her loss. A lone dive bomber — commonly attributed to a D4Y, though the identification is contested — also crippled the fleet carrier USS Franklin on 19 March 1945 in one of the US Navy’s worst carrier disasters.
How many D4Y Suisei survive today?
Very few. One largely complete airframe is displayed at the Yūshūkan museum in Tokyo, and the Planes of Fame Air Museum in California holds a restored D4Y3. Roughly 2,038 were built, but almost all were lost in combat, expended in kamikaze attacks, or scrapped after the war.
Was the D4Y used for kamikaze attacks?
Yes. As trained aircrew and fuel ran out, many surviving Suiseis were assigned to special-attack (kamikaze) units, and the single-seat D4Y4 was built specifically for the role. The last Japanese air sortie of the war, on 15 August 1945, was a flight of D4Ys led by Vice Admiral Matome Ugaki.
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Related Aircraft

Continue the tour

The PredecessorAichi D3A “Val”The rugged fixed-gear dive bomber the fast Suisei was meant to replace — the aircraft that struck Pearl Harbor.Read the D3A Val storyThe PartnerNakajima B5N “Kate”The Suisei’s carrier stablemate — the torpedo bomber that helped sink American carriers early in the Pacific War.Read the B5N Kate storyThe EscortMitsubishi A6M ZeroThe legendary fighter that escorted Japan’s carrier strikes — and, like the Suisei, ended the war as a kamikaze.Read the A6M Zero story
Sources & Further Reading

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