Nakajima B6N Tenzan (Jill) — History, Specs & Stories

Nakajima B6N Tenzan Jill Imperial Japanese Navy carrier torpedo bomber in flight
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Nakajima B6N Tenzan
“Jill”

Japan’s fastest carrier torpedo bomber — the powerful successor to the B5N Kate that reached the fleet in 1943, just as the crews and carriers it was built for were slipping away.

482 km/hTop speed · ~299 mph
~1,268Aircraft built · all variants
3Crew · pilot, observer, gunner
1941–1945First flight · end of the war
Photo: U.S. Navy · Public domain
RoleCarrier-based torpedo & attack bomberEraWorld War IIMotorMitsubishi Kasei 25 radialOriginJapan · NakajimaStatusRetired · one survivorCan you fly a B6N Tenzan today?
La historia

The Nakajima B6N Tenzan: Japan’s torpedo bomber that arrived too late

By 1939 the Imperial Japanese Navy’s frontline carrier torpedo bomber was the Nakajima B5N “Kate” — the aircraft that would help sink battleships at Pearl Harbor. Even as the Kate went to war, Nakajima was already designing its replacement. The result was the B6N Tenzan (“Heavenly Mountain”): a bigger, heavier, far more powerful machine meant to carry a torpedo faster and further than any carrier attack aircraft Japan had ever flown.

On paper it was a clean evolution — the same three-man crew, the same folding wings for carrier stowage — but built around a giant new radial engine and a redesigned airframe. In the air it became the fastest carrier torpedo bomber Japan ever fielded. Yet it was born into trouble. The engine chosen for it, Nakajima’s own Mamoru, was powerful but unreliable, and development slipped almost two years behind schedule.

When the Ministry of Munitions ordered Nakajima to abandon the Mamoru and concentrate its factories on other engines, the whole programme had to be re-engined around the Mitsubishi Kasei 25. That produced the definitive B6N2 — but it cost precious time. The engine and its large four-blade propeller generated so much torque that the vertical tail had to be canted slightly to one side just to keep the aircraft flying straight.

By the time the Tenzan finally reached the fleet in 1943, the war had already turned. The superb carrier aircrews that had rampaged across the Pacific in 1941–42 had been gutted at Midway and bled white over the Solomons. The Tenzan was a fine aeroplane flown, increasingly, by half-trained crews against an enemy whose fighters, radar and anti-aircraft fire had all improved dramatically.

The reckoning came in June 1944 at the Battle of the Philippine Sea — the “Great Marianas Turkey Shoot.” Dozens of Tenzans were launched against the US fleet; most were shot down by Hellcats before they could line up a shot, and not one of their torpedoes struck home. At Leyte Gulf that October the story repeated. Increasingly the type flew from land bases, and in the war’s final months some were expended in kamikaze attacks off Okinawa.

Around 1,268 were built — the exact figure is contested. To the Allies it was simply “Jill.” By most measures it was a good aircraft: fast, long-legged and hard-hitting on paper. Its tragedy was timing — a first-class torpedo bomber delivered to a naval air arm that no longer had the trained crews or the carriers to use it. Today a single B6N2 survives, held by the Smithsonian’s National Air and Space Museum: the last Tenzan in the world.

A first-class torpedo bomber, delivered to a fleet that had already lost the crews to fly it.The Tenzan’s tragedy — the right aircraft, two years too late
01The Nakajima B6N Tenzan’s engine crisis: how a troubled radial reshaped the whole aircraft

The Tenzan was designed around Nakajima’s new Mamoru 11, a 14-cylinder radial of about 1,800 hp chosen for its fuel economy and room to grow. But the Mamoru proved troublesome, and Nakajima’s factories were already stretched. When the Ministry of Munitions ordered the company to stop building the Mamoru after only around 130 B6N1s and switch to the Mitsubishi Kasei 25, the airframe had to be adapted to a different engine mid-programme — the change that created the mass-produced B6N2.

The powerful engine brought its own quirk. Torque from the big four-blade propeller pulled the aircraft off-heading so strongly that Nakajima canted the vertical tail a few degrees to port to compensate — a distinctive, slightly lopsided look. Combined with structural fixes forced by carrier landing trials, the engine saga is the main reason a design first flown in early 1941 did not reach the fleet in numbers until 1943.

Design & Engineering

What makes the B6N Tenzan special

01

A bigger, faster successor to the Kate

The Tenzan kept the B5N’s three-seat layout and carrier-friendly folding wings but wrapped them around a much larger radial engine and a cleaner, heavier airframe. The payoff was speed and reach: at roughly 482 km/h it was the fastest carrier torpedo bomber Japan ever put to sea, able to carry a full torpedo across long over-water distances.

02

The engine that forced a redesign

Planned around the unreliable Nakajima Mamoru and then re-engined with the Mitsubishi Kasei 25 of about 1,850 hp, the Tenzan carried the marks of its troubled birth. Engine torque was so strong that the fin was canted to one side, and the delay pushed the aircraft into service two years late.

03

Built for the torpedo, armed for the fleet

Its reason for being was the Type 91 aerial torpedo — roughly 800 kg slung under the belly — or an equivalent bomb load. A crew of three worked the aircraft: pilot, observer and a radio-operator/gunner defending the tail, with later marks carrying a heavier dorsal gun and, on some aircraft, air-to-surface radar.

02The Nakajima B6N Tenzan’s carrier problem: why it needed Japan’s newest decks

The Tenzan was heavier and faster-landing than the Kate it replaced, and early carrier trials exposed structural and arrestor-hook problems that had to be fixed before it could operate safely. By the time those fixes were made, many of the large fleet carriers it had been designed for had already been sunk at Midway and in the 1942–43 battles. The aircraft increasingly flew from the newer, larger carriers that survived — and, more and more, from land bases — rather than the sea-going striking force it was conceived to equip.

03The Nakajima B6N Tenzan’s defences: three men, a torpedo and a losing fight for the sky

Like most torpedo bombers, the Tenzan was fast for its class but lightly defended — one or two rifle-calibre machine guns, upgraded to a 13 mm dorsal weapon on the B6N2a. Against the disciplined Hellcat combat air patrols and radar-directed anti-aircraft fire of the 1944 US fleet, that was not enough. A torpedo run demanded a long, low, straight approach at the target, exactly the profile that made the aircraft easiest to shoot down. The Tenzan’s combat record is less a story of its own failings than of a good aircraft flown into an impossible tactical situation.

Datos técnicos

Full B6N Tenzan specifications

Airframe & Performance

Multitud
3 (pilot, observer, radio-operator/gunner)
Longitud
~10.87 m (B6N2)
Envergadura
~14.89 m
Altura
~3.80 m
Max takeoff weight
~5,650 kg
Max speed
~482 km/h (299 mph) at ~4,900 m
Velocidad de crucero
~330 km/h
Rango
~1,750 km normal · ~3,000 km ferry
Techo de servicio
~9,000 m
First flight
14 March 1941

Propulsion, Armament & Cost

Engine (B6N2)
Mitsubishi Kasei 25 (MK4T) 14-cyl radial
Power
~1,850 hp at takeoff
Engine (B6N1)
Nakajima Mamoru 11 (~1,800 hp)
Main weapon
1 × Type 91 torpedo (~800 kg) or bombs
Defensive guns
1–2 × 7.7 mm (13 mm dorsal on B6N2a)
Allied reporting name
“Jill”
Built
~1,268 (all variants, 1943–45)
Unit cost
No reliable public figure (wartime state production)
Cost per flight hour
No reliable public figure exists
04The Nakajima B6N Tenzan’s cost: why no reliable price exists

The Tenzan was a wartime product of the Japanese state, built for the Imperial Japanese Navy and never sold on any open market, so a meaningful flyaway unit price simply does not exist in the public record. Period Japanese figures were denominated in wartime yen under a controlled economy and do not convert into a comparable modern dollar cost. There is likewise no credible cost-per-flight-hour figure for the type — the concept was not tracked the way it is for modern aircraft, and no reliable operating-cost accounting survives. Any precise price attached to a B6N should be treated as an estimate, not a sourced fact.

Timeline

From the Kate’s successor to the war’s last torpedo runs

1939

The requirement

The Navy issues a specification for a faster, longer-ranged carrier attack aircraft to succeed the B5N Kate.

1941

First flight

The prototype flies on 14 March 1941 with the Nakajima Mamoru engine — the start of a long, troubled development.

1943

Enters service

After the switch to the Mitsubishi Kasei engine and carrier-trial fixes, the B6N2 finally reaches the fleet.

Nov 1943

Combat debut

Tenzans fly their first strikes over the Solomons and Bougainville against US carrier forces raiding Rabaul.

Jun 1944

The Philippine Sea

In the “Marianas Turkey Shoot” most attacking Tenzans are shot down; none of their torpedoes hit.

Oct 1944

Leyte & Formosa

Land- and carrier-based Tenzans attack US Task Force 38 at Leyte Gulf and in the Formosa Air Battle, at heavy cost.

1945

Kamikaze

With the fleet gone, surviving Tenzans are thrown into suicide attacks off Okinawa in the war’s final months.

1981

The last survivor

The Smithsonian acquires a B6N2 recovered after the war — today the only complete Tenzan left in the world.

Stories & Eyewitnesses

From the hangar deck: twelve B6N Tenzan stories

Origins

Built to replace the Kate

The B5N Kate helped sink battleships at Pearl Harbor; the Tenzan was meant to do the same job faster.

Read the full story
When the Tenzan was designed, the Nakajima B5N “Kate” was the best carrier torpedo bomber in the world — it had crippled the US battle line at Pearl Harbor and helped sink the carriers Yorktown, Lexington and Hornet. The B6N was conceived as a straight successor: same three-man crew and folding wings, but bigger, faster and longer-ranged, so that Japan’s carriers could strike from further out and get home again.
The name

Why “Heavenly Mountain”?

Tenzan is named for a mountain range; to the Allies it was just “Jill.”

Read the full story
“Tenzan” means “Heavenly Mountain,” the Japanese reading of the Tien Shan range in Central Asia — part of a naval tradition of naming aircraft after natural features. Allied intelligence, which could not rely on Japanese names, assigned reporting codes instead: torpedo bombers got female names, so the B6N became “Jill” — the name under which most Allied airmen knew it.
Engineering

The engine that changed twice

Designed around the Nakajima Mamoru, the Tenzan had to be re-engined with the Mitsubishi Kasei.

Read the full story
The Tenzan was built around Nakajima’s Mamoru radial, chosen for its fuel economy and growth potential. But the engine was unreliable and Nakajima’s plants were overstretched, so the Ministry of Munitions ordered production switched to the Mitsubishi Kasei 25 after only around 130 aircraft. Re-engineering a design mid-production cost months the Navy could not spare and split the type into the early B6N1 and the mass-produced B6N2.
Handling

The tail that leans

Engine torque was so strong the vertical fin was canted to one side to fly straight.

Read the full story
The Tenzan’s big engine and four-blade propeller produced enormous torque, dragging the nose off heading on takeoff and in the climb. Rather than fight it with constant rudder, Nakajima’s engineers simply built the correction into the airframe, angling the vertical tail a few degrees to one side. The result was a subtly lopsided-looking fin — a permanent reminder of the power the airframe was wrapped around.
Carrier trials

Too heavy for the old decks

Structural and arrestor problems meant the Tenzan needed Japan’s newer, larger carriers.

Read the full story
Heavier and faster-landing than the Kate, the Tenzan strained carrier arrestor gear and revealed structural weaknesses during deck trials that had to be reinforced before it could serve. By then many of the fleet carriers it had been designed for were already at the bottom of the Pacific, so the type increasingly flew from the few large carriers that remained — and, more and more, from land airfields.
Combat debut

First blood over the Solomons

The Tenzan went to war in November 1943 against US carriers raiding Rabaul.

Read the full story
The Tenzan first saw action in November 1943, flying against the US carrier task forces striking the great Japanese base at Rabaul and the Bougainville landings. These early actions showed both the aircraft’s speed and the growing danger it faced: American fighters were numerous and well-directed, and the experienced Japanese aircrews of 1942 were largely gone.
Philippine Sea

The Marianas Turkey Shoot

In June 1944 Tenzan squadrons were annihilated before they could line up their torpedoes.

Read the full story
At the Battle of the Philippine Sea in June 1944, dozens of Tenzans were launched against the US fleet in what American aircrew nicknamed the “Great Marianas Turkey Shoot.” Radar gave the defenders early warning, and disciplined Hellcat patrols cut the incoming strikes to pieces. Of the Tenzans that attacked, most were shot down and not one of their torpedoes struck a ship — a disaster from which Japanese carrier aviation never recovered.
Leyte Gulf

No hits, heavy losses

At Leyte the Tenzan again failed to break through American fighter and radar defences.

Read the full story
By the Battle of Leyte Gulf in October 1944, Japan’s carriers were being used as bait and most Tenzans flew from land. Committed against Task Force 38, the torpedo bombers were again unable to penetrate the wall of American fighters and flak in any strength. The aircraft was still fast and capable, but the tactical situation had become hopeless.
Formosa

Night torpedo runs

Land-based Tenzans attacked Task Force 38 in the Formosa Air Battle of October 1944.

Read the full story
In the Formosa Air Battle of October 1944, land-based Tenzans joined massed torpedo attacks on the US carriers, pressing home strikes by day and night. Japanese communiques claimed a great victory; in reality the American fleet suffered only minor damage while Japan lost hundreds of aircraft and irreplaceable crews — a pattern the Tenzan could not break.
Radar

Hunting ships in the dark

Some late Tenzans carried air-to-surface radar for night anti-shipping work.

Read the full story
As the daylight sky grew lethal, the Japanese Navy turned increasingly to night attacks, and some late-production Tenzans were reportedly fitted with air-to-surface radar to locate ships in darkness. It was a sign of how far the balance had shifted: an aircraft designed to lead massed daylight carrier strikes was now creeping in alone, at night, to survive at all.
Kamikaze

The last missions

In 1945 surviving Tenzans were expended in suicide attacks off Okinawa.

Read the full story
By 1945, with carriers and trained crews all but gone, many surviving Tenzans were assigned to kamikaze units. Off Okinawa they were flown on one-way missions against the US invasion fleet — a grim final role for an aircraft that had been built to deliver a torpedo and fly home.
Survivor

The last Tenzan on Earth

One B6N2 survives at the Smithsonian — the only complete example left in the world.

Read the full story
Of the roughly 1,268 Tenzans built, a single complete aircraft survives. Recovered by the US Navy after the war and acquired by the Smithsonian’s National Air and Space Museum in 1981, this B6N2 is the last of its kind anywhere — the only surviving example of Japan’s final wartime carrier torpedo bomber.
Gallery

The B6N Tenzan in pictures

A Nakajima B6N Tenzan attacking low over the sea off Truk, April 1944.
A Nakajima B6N Tenzan attacking low over the sea off Truk, April 1944.Photo: U.S. Navy · Public domain · via Wikimedia Commons
B6N2 Tenzan of the 752nd Kkutai flying in formation.
B6N2 Tenzan of the 752nd Kōkutai flying in formation.Photo: Imperial Japanese Navy · Public domain · via Wikimedia Commons
A Tenzan banking on a torpedo run the long greenhouse canopy is clearly visible.
A Tenzan banking on a torpedo run — the long “greenhouse” canopy is clearly visible.Photo: Imperial Japanese Navy · Public domain · via Wikimedia Commons
A B6N2 Tenzan on the ground before takeoff.
A B6N2 Tenzan on the ground before takeoff.Photo: Imperial Japanese Navy · Public domain · via Wikimedia Commons
A Tenzan drops its torpedo off USS Essex (CV-9), October 1944.
A Tenzan drops its torpedo off USS Essex (CV-9), October 1944.Photo: U.S. Navy / National Museum of Naval Aviation · Public domain · via Wikimedia Commons
A Tenzan is hit and shot down off Kwajalein, 4 December 1943.
A Tenzan is hit and shot down off Kwajalein, 4 December 1943.Photo: U.S. Navy · Public domain · via Wikimedia Commons
Watch

The B6N Tenzan in motion

Rare wartime footage of the Nakajima B6N Tenzan in flight and operating from the deck — one of the few moving-picture records of Japan’s last carrier torpedo bomber. Archival compilation via Aviation Videos Archives.

Operations

Where the B6N Tenzan fought

Combat Record

The score that defines the B6N Tenzan

The Tenzan’s combat record is a hard one to read, because its story is less about what it did than about when it arrived. Technically capable and fast for its class, it reached the fleet only after Japan had lost the experienced carrier aircrews and the massed carrier decks it was built to serve. In its two great battles it was cut apart before it could strike.

Nov 1943Combat debut over the Solomons & Bougainville
~14 of 44Tenzans survived the Philippine Sea strike (June 1944)
0 hitsNone of their torpedoes struck home at the Philippine Sea

Compare the combat record of every military aircraft. Figures reflect the most commonly cited accounts and are hedged where sources differ.

Questions & Answers

Everything people ask about the Nakajima B6N Tenzan

Can I fly in a Nakajima B6N Tenzan?
No — the Tenzan has not flown since the war, and only a single static example survives, in a museum. There is no airworthy B6N anywhere in the world, and MiGFlug has never operated the type. You can, however, fly in several genuine ex-military jets today — see migflug.com/flights-prices/.
What does “Tenzan” mean, and why was it called “Jill”?
“Tenzan” means “Heavenly Mountain,” after the Tien Shan range. The Allied name “Jill” came from the wartime reporting-code system, which gave Japanese torpedo bombers female names so aircrew could identify types quickly without knowing the Japanese designations.
How fast was the B6N Tenzan?
About 482 km/h (299 mph) at altitude — the fastest carrier torpedo bomber Japan fielded, and noticeably quicker than the B5N Kate it replaced. Speed, however, could not save it from radar-directed fighter defences in 1944.
Why did the B6N need a new engine?
It was designed around the Nakajima Mamoru radial, which proved unreliable while Nakajima’s factories were overstretched. The Ministry of Munitions ordered a switch to the Mitsubishi Kasei 25 after only about 130 aircraft, creating the mass-produced B6N2 — but the change delayed the type by roughly two years.
How many B6N Tenzans were built?
Commonly cited figures are around 1,268 in total — roughly 130 early B6N1s with the Mamoru engine and about 1,130 Kasei-powered B6N2/B6N2a aircraft. The exact number varies between sources.
Did the B6N Tenzan sink any ships?
Very few, if any, of note. In its major actions — the Philippine Sea and Leyte Gulf — Tenzan torpedo strikes were shattered by American fighters and flak before they could hit, and at the Philippine Sea none of their torpedoes struck home. Its failure was one of timing and circumstance far more than of design.
Are there any surviving B6N Tenzans?
Just one complete aircraft. A B6N2 recovered after the war is held by the Smithsonian’s National Air and Space Museum, which acquired it in 1981. It is the only surviving Tenzan in the world.
How was the B6N different from the B5N Kate?
The Tenzan kept the Kate’s three-seat, folding-wing carrier layout but was larger, heavier and far more powerful, giving more speed and range. It was a genuine improvement — it simply arrived after the naval air war had already turned against Japan.
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Related Aircraft

Continue the tour

The PredecessorNakajima B5N KateThe torpedo bomber the Tenzan was built to replace — and the aircraft that struck the battleships at Pearl Harbor.Read the B5N Kate storyThe Dive-BomberYokosuka D4Y SuiseiThe fast carrier dive-bomber that flew alongside the Tenzan in the desperate carrier battles of 1944.Read the D4Y Suisei storyThe EscortMitsubishi A6M ZeroThe legendary fighter that escorted Japan’s torpedo and dive bombers across the Pacific.Read the A6M Zero story
Sources & Further Reading

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