Nakajima B6N Tenzan (Jill)
Imperial Japan (1943)
The promising Nakajima B6N torpedo bomber of WW2 - codenamed Jill by the Allies - arrived at a time when air superiority for the Japanese had slipped away.
Detailing the development and operational history of the Nakajima B6N Tenzan (Jill) Carrier-Borne Torpedo Bomber Aircraft. Entry last updated on 4/3/2017. Authored by Staff Writer. Content ©www.MilitaryFactory.com
The Nakajima Aircraft Company of Japan had been delivering naval-minded aircraft since 1927 (the A1N) and would produce a slew of designs leading up to, and during, the Grand War. In 1937, the prototype that would become the B5N torpedo and dive bomber (codenamed "Kate" by the Allies) flew for the first time. Service entry came a time later and 1,149 examples of this monoplane were produced. With prewar origins, a successor was developed by Nakajima in what became the B6N "Tenzan" ("Heavenly Mountain") and its own first flight was had during March of 1941 but a lengthy development phase meant that service entry was not until August of 1943. Some 1,268 examples of this design followed and the line was codenamed "Jill" by the Allies. The aircraft led a limited operational existence for air superiority had switched to the Allies as the war progressed towards it conclusion in 1945.
The B6N was designed to shore up the limitations discovered operationally with the earlier B5N series - namely performance and range. This led to the Imperial Japanese Navy (IJN) developing a new specification for a carrier-based attack platform of an all-modern design capable of hauling warloads up to 1,800 pounds out to 1,200 miles at cruising speeds of 230 miles per hour. Maximum speed was near the 300 mile-per-hour mark. The new Nakajima "Mamori 11" series 14-cylinder air-cooled radial engine would power the design which would include an operating crew of three made up of a pilot, radioman/gunner and bombardier (doubling as the flight's navigator). Initially it was expected that the Mitsubishi "Kasei" engine would be used - but Nakajima engineers successfully sold authorities on their in-house development instead.
This led to an aircraft of largely conventional design - a long, slender fuselage was required for the performance and hauling capability expected. A single engine, fitted to the nose, would power the airframe. The crew of three would be seated inline under a long-running, heavily-glazed canopy (greenhouse-style) assembly offering exceptional vision around the aircraft. A defensive position was fitted dorsally at the rear of the canopy section with a sole 7.7mm Type 92 machine gun on a trainable mounting being fitted. The torpedo load would be held externally under fuselage centerline. The wing mainplanes were low-mounted and fitted slightly ahead of midships. The tail unit was conventional with its single vertical fin and low-mounted horizontal planes. The undercarriage was of a "tail-dragger" arrangement with the main legs retractable under the wing elements. Dimensions conformed to the hangar elevators of Japanese carriers of the day and Fowler flaps were used to slow the aircraft's attack run and during landing actions on carrier decks. The Nakajima engine powered a four-bladed propeller unit.
The prototype went airborne on March 14th, 1941 though it was not an immediate success - the powerful engine produced a greater torque effect than expected and caused the aircraft to want to roll over consistently. This led to changes to the vertical tail unit but issues with the new engine were persistent as overheating and excessive vibration were noted through test flights. Modifications were had but served to also delay the program, and the aircraft was officially trialled on Japanese carrier decks during 1942. At the end of its evaluation phase, the engine proved suitable for operational service and a ventral 7.7mm machine gun position was added to protect the aircraft's vulnerable underside from trailing interceptors. This position was accessed by way of a tunnel and the machine gun was retractable to maintain aerodynamics when no in use.
In the early half of 1943, the design was contracted for serial production as the "B6N1". The aircraft would carry a single torpedo into battle, such was the standard of the day, and self-sealing fuel tanks were amazingly not a part of the finalized design - increasing operational ranges but making the aircraft highly susceptible to enemy fire of all kinds. Once production got underway and over 100 had been completed, it was decided to switch the temperamental engines with the originally-intended Mitsubishi Kasei 25 series of 1,850 horsepower. This led to a slight lengthening of the nose section to accommodate both the engine and a change to the airframe's natural Center-of-Gravity (CoG). These changes then produced the new designation of "B6N2" (Model 12).
Every third B6N2 was then outfitted with surface search radar equipment which gave a flight group the capability to find and mark its own targets. 1,131 B6N2 models were produced in all, marking it as the definitive model of the series. The B6N2a (Model 12A) featured a revised defensive armament arrangement which substituted the 7.7mm Type 92 system with the larger-caliber 13mm Type 2 heavy model to help increase firepower.
The B6N2 featured an overall length of 10.8 meters, wingspan of 15 meters and a height of 3.8 meters. Its empty listed weight was 6,635 pounds against a Maximum Take-Off Weight (MTOW) of 12,450 pounds. Maximum speed from the Kasei 25 radial engine (1,850 horsepower at take-off) was 300 miles per hour with cruising speeds reaching 205 miles per hour. Range was a useful 1,900 miles along with a service ceiling of 29,650 feet. Its warload included a 1,760 pound torpedo or the equivalent in conventional drop bombs.
With the war situation for Japan turning worse with each passing month, and its carrier attack force more-or-less neutralized by the Allied offensives, it was thought to create a land-based version of this aircraft which led to the "B6N3" (Model 13) designation. These would carry the Mitsubishi MK4T-C "Kasei 25c engine of 1,850 horsepower and feature a revised undercarriage for land-based service. However, the end of the war came too quickly for this variant and only two prototypes were ever completed.
The prototype went airborne on March 14th, 1941 though it was not an immediate success - the powerful engine produced a greater torque effect than expected and caused the aircraft to want to roll over consistently. This led to changes to the vertical tail unit but issues with the new engine were persistent as overheating and excessive vibration were noted through test flights. Modifications were had but served to also delay the program, and the aircraft was officially trialled on Japanese carrier decks during 1942. At the end of its evaluation phase, the engine proved suitable for operational service and a ventral 7.7mm machine gun position was added to protect the aircraft's vulnerable underside from trailing interceptors. This position was accessed by way of a tunnel and the machine gun was retractable to maintain aerodynamics when no in use.
In the early half of 1943, the design was contracted for serial production as the "B6N1". The aircraft would carry a single torpedo into battle, such was the standard of the day, and self-sealing fuel tanks were amazingly not a part of the finalized design - increasing operational ranges but making the aircraft highly susceptible to enemy fire of all kinds. Once production got underway and over 100 had been completed, it was decided to switch the temperamental engines with the originally-intended Mitsubishi Kasei 25 series of 1,850 horsepower. This led to a slight lengthening of the nose section to accommodate both the engine and a change to the airframe's natural Center-of-Gravity (CoG). These changes then produced the new designation of "B6N2" (Model 12).
Every third B6N2 was then outfitted with surface search radar equipment which gave a flight group the capability to find and mark its own targets. 1,131 B6N2 models were produced in all, marking it as the definitive model of the series. The B6N2a (Model 12A) featured a revised defensive armament arrangement which substituted the 7.7mm Type 92 system with the larger-caliber 13mm Type 2 heavy model to help increase firepower.
The B6N2 featured an overall length of 10.8 meters, wingspan of 15 meters and a height of 3.8 meters. Its empty listed weight was 6,635 pounds against a Maximum Take-Off Weight (MTOW) of 12,450 pounds. Maximum speed from the Kasei 25 radial engine (1,850 horsepower at take-off) was 300 miles per hour with cruising speeds reaching 205 miles per hour. Range was a useful 1,900 miles along with a service ceiling of 29,650 feet. Its warload included a 1,760 pound torpedo or the equivalent in conventional drop bombs.
With the war situation for Japan turning worse with each passing month, and its carrier attack force more-or-less neutralized by the Allied offensives, it was thought to create a land-based version of this aircraft which led to the "B6N3" (Model 13) designation. These would carry the Mitsubishi MK4T-C "Kasei 25c engine of 1,850 horsepower and feature a revised undercarriage for land-based service. However, the end of the war came too quickly for this variant and only two prototypes were ever completed.
Our Data Modules allow for quick visual reference when comparing a single entry against contemporary designs. Areas covered include general ratings, speed assessments, and relative ranges based on distances between major cities.
Relative Maximum Speed Rating
Hi: 300mph
Lo: 150mph
This entry's maximum listed speed (299mph).
Graph average of 225 miles-per-hour.
Relative Operational Ranges
NYC
LON
LON
PAR
PAR
BER
BER
MOS
MOS
TOK
TOK
SYD
SYD
LAX
LAX
NYC
Graph showcases the Nakajima B6N2 Tenzan (Jill)'s operational range (on internal fuel) when compared to distances between major cities.
Aviation Era Impact
Useful in showcasing the era cross-over of particular aircraft/aerospace designs.
Unit Production Comparison
Comm. Market HI*: 44,000 units
Military Market HI**: 36,183 units
1266
1266
* Commercial Market High belongs to Cessna 172.
** Military Market High belongs to Ilyushin Il-2.
Altitude Visualization
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Supported Mission Types:
Air-to-Air
Interception
Unmanned
Ground Attack
Close-Air Support
Training
Anti-Submarine
Anti-Ship
Airborne Early Warning
MEDEVAC
Electronic Warfare
Maritime/Navy
Aerial Tanker
Utility/Transport
Passenger Industry
VIP Travel
Business Travel
Search/Rescue
Recon/Scouting
Special Forces
X-Plane/Development
National Origin: Imperial Japan
Service Year: 1943
Classification Type: Carrier-Borne Torpedo Bomber Aircraft
Manufacturer(s): Nakajima - Japan
Production Units: 1,266
Global Operators:
Imperial Japan
Imperial Japan
Unless otherwise noted the presented statistics below pertain to the Nakajima B6N2 Tenzan (Jill) model. Common measurements, and their respective conversions, are shown when possible.
Operational
CREW
Personnel
3
Dimension
LENGTH
Feet
35.66 ft
Meters
10.87 m
Dimension
WIDTH
Feet
48.85 ft
Meters
14.89 m
Dimension
HEIGHT
Feet
12.47 ft
Meters
3.8 m
Weight
EMPTY
Pounds
6,636 lb
Kilograms
3,010 kg
Weight
LOADED
Pounds
12,456 lb
Kilograms
5,650 kg
1 x Mitsubishi MK4T Kasei 25 radial piston engine developing 1,850 horsepower.
Performance
SPEED
Miles-per-Hour
299 mph
Kilometers-per-Hour
481 kph
Knots
260 kts
Performance
RANGE
Miles
1,085 mi
Kilometers
1,746 km
Nautical Miles
943 nm
Performance
CEILING
Feet
29,659 ft
Meters
9,040 m
Miles
5.62 mi
Performance
CLIMB RATE
Feet-per-Minute
1,577 ft/min
Meters-per-Minute
481 m/min
Armament - Hardpoints (3):
STANDARD:
1 x 7.7mm Type 97 machine gun in ventral position
1 x 13mm Type 2 machine gun in rear trainable mounting
OPTIONAL:
Mission-specific ordnance can include a combat load of 1 x 1,764lb torpedo bombs equivalent.
STANDARD:
1 x 7.7mm Type 97 machine gun in ventral position
1 x 13mm Type 2 machine gun in rear trainable mounting
OPTIONAL:
Mission-specific ordnance can include a combat load of 1 x 1,764lb torpedo bombs equivalent.
Supported Weapon Systems:
Variants:
Series Model Variants
• B6N1 - "Model 11"; initial production model of which 133 were produced plus two prototypes.
• B6N2 - "Model 12"; improved B6N1 model of which some 1,133 examples were produced before war's end; fitted with Mitsubishi MK4T Kasei 25 engine generating 1,850 horsepower.
• B6N2a - "Model 12A"; 1 x 13.2mm Type 2 machine gun replaced 1 x 7.7mm Type 97 in rear cockpit.
• B6N3 - "Model 13"; Prototype model based on the B6N2a; fitted with Mitsubishi MK4T-C Kasei 25c engine developing 1,850 horsepower; landing gear systems updated for land-based usage.
• B6N1 - "Model 11"; initial production model of which 133 were produced plus two prototypes.
• B6N2 - "Model 12"; improved B6N1 model of which some 1,133 examples were produced before war's end; fitted with Mitsubishi MK4T Kasei 25 engine generating 1,850 horsepower.
• B6N2a - "Model 12A"; 1 x 13.2mm Type 2 machine gun replaced 1 x 7.7mm Type 97 in rear cockpit.
• B6N3 - "Model 13"; Prototype model based on the B6N2a; fitted with Mitsubishi MK4T-C Kasei 25c engine developing 1,850 horsepower; landing gear systems updated for land-based usage.