Nakajima B6N
Encyclopedia
The Nakajima B6N Tenzan (Japanese
: 中島 B6N 天山—"Heavenly Mountain", Allied reporting name
: "Jill") was the Imperial Japanese Navy
's standard carrier-borne torpedo bomber
during the final years of World War II
and the successor to the B5N "Kate"
. Due to its protracted development, a shortage of experienced pilots and the United States Navy
's achievement of air superiority by the time of its introduction, the B6N was never able to fully demonstrate its combat potential.
The B5N carrier torpedo-bomber's weaknesses had shown themselves early in the Second Sino-Japanese War
and, as well as updating that aircraft, the Imperial Japanese Navy began seeking a faster longer-ranged replacement. In December 1939 it issued a specification to Nakajima for a Navy Experimental 14-Shi Carrier Attack Aircraft capable of carrying the same external weapons load as the B5N. The new plane was to carry a crew of three (pilot, navigator/bombardier and radio operator/gunner) and be of low wing, cantilevered, all-metal construction (though control surfaces were fabric-covered). Further requirements included a top speed of 250 kn (304.4 mph; 490 km/h), a cruising speed of 200 kn (243.6 mph; 392 km/h) and a range of 1000 nmi (1,852 km) with an 800 kg (1,763.7 lb) bomb load or 2072 nmi (3,837.3 km) without external armament.
The Navy had requested installation of the proven Mitsubishi Kasei engine as the B6N's powerplant but Engineer Kenichi Matsumara insisted on using Nakajima's new 1870 hp Mamoru 11 14-cylinder air-cooled radial due to its lower fuel consumption and greater adaptability. This became an unfortunate choice as the Mamoru engine was plagued with mechanical defects and never achieved its expected power rating.
Constrained by the standard-sized aircraft elevators then in use on most Japanese carriers, designer Matsumara was obliged to use a wing similar in span and area as that of the B5N and to limit the aircraft's overall length to 11 m (36.1 ft). This latter restriction accounted for the B6N's distinctive swept-forward tail fin and rudder.http://www.j-aircraft.com/walk/john_ferguson/jill1stbrd.jpg The outer wing panels folded upward hydraulically, reducing the B6N's overall span from 14.9 m (48.9 ft) to approximately 6.3 m (20.7 ft) for minimal carrier stowage. In order to lessen increased wingloading due to the heavier powerplant, Fowler flaps were installed which could be extended beyond the wing's trailing edge. These were normally lowered to an angle of 20 degrees during take-off and 38 degrees when landing. Despite the use of these flaps, however, the B6N had a much higher stall speed than its predecessor.
The prototype B6N1 made its maiden flight on 14 March, 1941. Following continued testing, however, several problems became evident. In particular, the aircraft exhibited an alarming tendency to roll while in flight, the cause of which was traced to the extreme torque developed by the four-bladed propeller. To compensate, the aircraft's tail fin was thinned down and moved 2 degrees ten minutes to port. This modification greatly improved the plane's handling characteristics.
The B6N1's Mamoru 11 engine was found prone to severe vibrations and overheating at certain speeds and was at first judged too unreliable (an important consideration given that the plane was expected to fly long distances over open water). Following a series of modifications, though, the engine's performance was finally deemed promising enough that carrier acceptance trials were begun at the end of 1942. Subsequent test flights conducted aboard the carriers Ryuho and Zuikaku indicated the need to strengthen the tail hook mounting on the plane's fuselage. Some attempts were also made to use RATOG (rocket-assisted take-off gear) units on several B6N1s in order to qualify the aircraft for use on smaller carriers but the results were unsatisfactory.
The B6N1 was officially approved for production status in early 1943 and given the designation Navy Carrier Attack Aircraft Tenzan Model 11. Modifications based on testing of the initial prototypes included: the addition of a flexible Type 92 machine-gun in a ventral tunnel at the rear of the cockpit and a 7.7mm Type 97 machine-gun to the port wing (the latter was eventually deleted after the seventieth production aircraft); angling the torpedo mounting rack 2 degrees downward and adding torpedo stabilization plates to prevent the torpedo from bouncing during low-altitude release; strengthening of the main landing gear. A proposal by the designers to replace the B6N1's unprotected fuel tanks with self-sealing ones would have resulted in a 30% drop in fuel capacity, a loss in range the Navy decided was unacceptable.
After only 133 B6N1s had been produced by July 1943, the Japanese Ministry of Munitions ordered Nakajima to halt manufacture of the Mamoru 11 engine in order that the Navy reduce the number of different engines then in use. Pending availability of the 18-cylinder Nakajima Homare engine, Nakajima was asked to substitute the 1850 hp Mitsubishi MK4T Kasei 25 engine on the B6N1 airframe, the very engine the Navy had originally requested them to use. As the Mamoru 11 and Kasei 25 were similar in size, installation was relatively straightforward, requiring only that the nose be extended to maintain the aircraft's center of gravity and minor alterations to the oil cooler and air intakes on the engine cowling. A smaller 3.4 m (11.2 ft) diameter four-bladed propeller and shorter spinner were also installed at this time and a fixed tail wheel replaced the original retractable one, resulting in a small weight-savings. Finally, the single exhaust stacks on either side of the engine cowling were replaced with multiple smaller stubs to reduce glare at night. The resulting modification was designated Navy Carrier Attack Aircraft Tenzan Model 12 or B6N2.
Starting in the fall of 1943, one of every three B6N2s manufactured was equipped with 3-Shiki Type 3 air-to-surface radar for detecting enemy ships. Yagi antennas were installed along the wing leading edges and also protruded from the sides of the rear fuselage.
A final version of the aircraft, designated B6N3 Model 13, was planned for land-based use as, by this point in the war, all of Japan's large carriers had been sunk and those few smaller ones remaining lacked catapults for launching heavier carrier-borne aircraft like the B6N. Changes included installation of a Kasei Model 25c engine, a more streamlined engine cowling and crew canopy, strengthening of the main landing gear, a retractable tail wheel and removal of the tail hook. Two B6N3 prototypes were completed but Japan surrendered before this variant could be put into production.
By war's end in August 1945, Nakajima had completed a total of 1,268 B6Ns (almost all of them B6N2s) at its plants in Okawa in the Gumma district and at Handa in the Aichi district. Production never exceeded more than 90 planes per month.
Additional attacks mounted on 8 November and 11 November yielded less sanguine results and suffered heavy losses in return. Only 52 of the original 173 planes from First Carrier Division made it back to Truk on 13 November, among them just six B6N1 Tenzans out of the forty initially committed.
On 19 June 1944, the B6N made its carrier-borne combat debut at The Battle of the Philippine Sea
, operating in an environment where the U.S. Navy had virtually complete air superiority. Subsequently, it failed to inflict any significant damage whatsoever whilst taking heavy losses from the U.S. Navy's new F6F Hellcat fighter.
By this point, small improvements in the B6N's performance were amongst the least of the Japanese Navy's problems. When the new model became available in mid-1944, Japan had already lost most of its large carriers, and was becoming desperately short of experienced pilots. The vast majority of B6N2 operations therefore took place from land bases and failed to achieve any major successes. The planes were extensively used in the Battle of Okinawa
where they were also used for kamikaze
missions for the first time.
in Washington, D.C.
. It consists of one fuselage (minus powerplant) and a vertical stabilizer
.
Japanese language
is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...
: 中島 B6N 天山—"Heavenly Mountain", Allied reporting name
World War II Allied names for Japanese aircraft
The World War II Allied names for Japanese aircraft were reporting names, often described as codenames, given by Allied personnel to Imperial Japanese aircraft during the Pacific campaign of World War II. The names were used by Allied personnel to identify Japanese aircraft for reporting and...
: "Jill") was the Imperial Japanese Navy
Imperial Japanese Navy
The Imperial Japanese Navy was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes...
's standard carrier-borne torpedo bomber
Torpedo bomber
A torpedo bomber is a bomber aircraft designed primarily to attack ships with aerial torpedoes which could also carry out conventional bombings. Torpedo bombers existed almost exclusively prior to and during World War II when they were an important element in many famous battles, notably the...
during the final years of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
and the successor to the B5N "Kate"
Nakajima B5N
|-See also:-References:NotesBibliography* Bridgwater, H.C. and Peter Scott. Combat Colours Number 4: Pearl Harbor and Beyond, December 1941 to May 1942. Luton, Bedfordshire, UK: Guideline Publications, 2001. ISBN 0-9539040-6-7....
. Due to its protracted development, a shortage of experienced pilots and the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
's achievement of air superiority by the time of its introduction, the B6N was never able to fully demonstrate its combat potential.
Design and development
Second Sino-Japanese War
The Second Sino-Japanese War was a military conflict fought primarily between the Republic of China and the Empire of Japan. From 1937 to 1941, China fought Japan with some economic help from Germany , the Soviet Union and the United States...
and, as well as updating that aircraft, the Imperial Japanese Navy began seeking a faster longer-ranged replacement. In December 1939 it issued a specification to Nakajima for a Navy Experimental 14-Shi Carrier Attack Aircraft capable of carrying the same external weapons load as the B5N. The new plane was to carry a crew of three (pilot, navigator/bombardier and radio operator/gunner) and be of low wing, cantilevered, all-metal construction (though control surfaces were fabric-covered). Further requirements included a top speed of 250 kn (304.4 mph; 490 km/h), a cruising speed of 200 kn (243.6 mph; 392 km/h) and a range of 1000 nmi (1,852 km) with an 800 kg (1,763.7 lb) bomb load or 2072 nmi (3,837.3 km) without external armament.
The Navy had requested installation of the proven Mitsubishi Kasei engine as the B6N's powerplant but Engineer Kenichi Matsumara insisted on using Nakajima's new 1870 hp Mamoru 11 14-cylinder air-cooled radial due to its lower fuel consumption and greater adaptability. This became an unfortunate choice as the Mamoru engine was plagued with mechanical defects and never achieved its expected power rating.
Constrained by the standard-sized aircraft elevators then in use on most Japanese carriers, designer Matsumara was obliged to use a wing similar in span and area as that of the B5N and to limit the aircraft's overall length to 11 m (36.1 ft). This latter restriction accounted for the B6N's distinctive swept-forward tail fin and rudder.http://www.j-aircraft.com/walk/john_ferguson/jill1stbrd.jpg The outer wing panels folded upward hydraulically, reducing the B6N's overall span from 14.9 m (48.9 ft) to approximately 6.3 m (20.7 ft) for minimal carrier stowage. In order to lessen increased wingloading due to the heavier powerplant, Fowler flaps were installed which could be extended beyond the wing's trailing edge. These were normally lowered to an angle of 20 degrees during take-off and 38 degrees when landing. Despite the use of these flaps, however, the B6N had a much higher stall speed than its predecessor.
The prototype B6N1 made its maiden flight on 14 March, 1941. Following continued testing, however, several problems became evident. In particular, the aircraft exhibited an alarming tendency to roll while in flight, the cause of which was traced to the extreme torque developed by the four-bladed propeller. To compensate, the aircraft's tail fin was thinned down and moved 2 degrees ten minutes to port. This modification greatly improved the plane's handling characteristics.
The B6N1's Mamoru 11 engine was found prone to severe vibrations and overheating at certain speeds and was at first judged too unreliable (an important consideration given that the plane was expected to fly long distances over open water). Following a series of modifications, though, the engine's performance was finally deemed promising enough that carrier acceptance trials were begun at the end of 1942. Subsequent test flights conducted aboard the carriers Ryuho and Zuikaku indicated the need to strengthen the tail hook mounting on the plane's fuselage. Some attempts were also made to use RATOG (rocket-assisted take-off gear) units on several B6N1s in order to qualify the aircraft for use on smaller carriers but the results were unsatisfactory.
The B6N1 was officially approved for production status in early 1943 and given the designation Navy Carrier Attack Aircraft Tenzan Model 11. Modifications based on testing of the initial prototypes included: the addition of a flexible Type 92 machine-gun in a ventral tunnel at the rear of the cockpit and a 7.7mm Type 97 machine-gun to the port wing (the latter was eventually deleted after the seventieth production aircraft); angling the torpedo mounting rack 2 degrees downward and adding torpedo stabilization plates to prevent the torpedo from bouncing during low-altitude release; strengthening of the main landing gear. A proposal by the designers to replace the B6N1's unprotected fuel tanks with self-sealing ones would have resulted in a 30% drop in fuel capacity, a loss in range the Navy decided was unacceptable.
After only 133 B6N1s had been produced by July 1943, the Japanese Ministry of Munitions ordered Nakajima to halt manufacture of the Mamoru 11 engine in order that the Navy reduce the number of different engines then in use. Pending availability of the 18-cylinder Nakajima Homare engine, Nakajima was asked to substitute the 1850 hp Mitsubishi MK4T Kasei 25 engine on the B6N1 airframe, the very engine the Navy had originally requested them to use. As the Mamoru 11 and Kasei 25 were similar in size, installation was relatively straightforward, requiring only that the nose be extended to maintain the aircraft's center of gravity and minor alterations to the oil cooler and air intakes on the engine cowling. A smaller 3.4 m (11.2 ft) diameter four-bladed propeller and shorter spinner were also installed at this time and a fixed tail wheel replaced the original retractable one, resulting in a small weight-savings. Finally, the single exhaust stacks on either side of the engine cowling were replaced with multiple smaller stubs to reduce glare at night. The resulting modification was designated Navy Carrier Attack Aircraft Tenzan Model 12 or B6N2.
Starting in the fall of 1943, one of every three B6N2s manufactured was equipped with 3-Shiki Type 3 air-to-surface radar for detecting enemy ships. Yagi antennas were installed along the wing leading edges and also protruded from the sides of the rear fuselage.
A final version of the aircraft, designated B6N3 Model 13, was planned for land-based use as, by this point in the war, all of Japan's large carriers had been sunk and those few smaller ones remaining lacked catapults for launching heavier carrier-borne aircraft like the B6N. Changes included installation of a Kasei Model 25c engine, a more streamlined engine cowling and crew canopy, strengthening of the main landing gear, a retractable tail wheel and removal of the tail hook. Two B6N3 prototypes were completed but Japan surrendered before this variant could be put into production.
By war's end in August 1945, Nakajima had completed a total of 1,268 B6Ns (almost all of them B6N2s) at its plants in Okawa in the Gumma district and at Handa in the Aichi district. Production never exceeded more than 90 planes per month.
Operational history
The B6N Tenzan began reaching front-line units in August 1943 but only in small numbers. The intent was to gradually replace all of the older B5N Kate torpedo planes then operating aboard the carriers of the Third Fleet at Truk Atoll in the Caroline Islands. However, the B6Ns were prematurely committed to battle when increased Allied naval activity in the Solomon Islands indicated a likely invasion at Bougainville. In response to this threat, the IJN initiated Operation Ro. This involved reinforcing land-based air units at Rabaul with 173 carrier aircraft from First Carrier Division (Zuikaku, Shokaku and Zuiho), including forty B6Ns. These aircraft were flown from Truk to Rabaul between 28 October and 1 November. On 5 November fourteen B6N1s, escorted by four Zero fighters, were sent to attack American shipping anchored off Bougainville. Four B6N1s were lost and no actual hits were scored, yet returning Japanese pilots claimed to have sunk one large and one medium carrier, two large cruisers and two other cruisers or large destroyers. This was considered an unusually auspicious debut for the new warplane.Additional attacks mounted on 8 November and 11 November yielded less sanguine results and suffered heavy losses in return. Only 52 of the original 173 planes from First Carrier Division made it back to Truk on 13 November, among them just six B6N1 Tenzans out of the forty initially committed.
On 19 June 1944, the B6N made its carrier-borne combat debut at The Battle of the Philippine Sea
Battle of the Philippine Sea
The Battle of the Philippine Sea was a decisive naval battle of World War II which effectively eliminated the Imperial Japanese Navy's ability to conduct large-scale carrier actions. It took place during the United States' amphibious invasion of the Mariana Islands during the Pacific War...
, operating in an environment where the U.S. Navy had virtually complete air superiority. Subsequently, it failed to inflict any significant damage whatsoever whilst taking heavy losses from the U.S. Navy's new F6F Hellcat fighter.
By this point, small improvements in the B6N's performance were amongst the least of the Japanese Navy's problems. When the new model became available in mid-1944, Japan had already lost most of its large carriers, and was becoming desperately short of experienced pilots. The vast majority of B6N2 operations therefore took place from land bases and failed to achieve any major successes. The planes were extensively used in the Battle of Okinawa
Battle of Okinawa
The Battle of Okinawa, codenamed Operation Iceberg, was fought on the Ryukyu Islands of Okinawa and was the largest amphibious assault in the Pacific War of World War II. The 82-day-long battle lasted from early April until mid-June 1945...
where they were also used for kamikaze
Kamikaze
The were suicide attacks by military aviators from the Empire of Japan against Allied naval vessels in the closing stages of the Pacific campaign of World War II, designed to destroy as many warships as possible....
missions for the first time.
Variants
- B6N1 : Prototypes - Engine Nakajima NK7A Mamoru 11 of 1,394 kW (1,870 hp), four-blade propeller. Two examples built.
- B6N1 Tenzan Navy Carrier Based-Attack Bomber, Model 11: First series model. 135 built.
- B6N2 Model 12: Main production model, featured Mitsubishi MK4T Kasei 25 of 1,380 kW (1,850 hp).
- B6N2a Model 12A: Revised tail armament. 7.7 mm (.303 in) Type 97 machine gunType 97 Light Machine GunThe was the standard machine gun used in tanks and armored vehicles of the Imperial Japanese Army during World War II, and also as a light machine gun by infantry forces.-Development:...
, replaced with one 13.2 mm Type 2 machine gun. - B6N3 Model 13 Prototypes: Engine Mitsubishi MK4T-C Kasei 25c of 1,380 kW (1,850 hp). Modified landing gear for operating from land bases; two B6N2a converted in factory.
- Total Production (all versions): 1,268 examples.
Survivors
Today only one B6N remains in existence and is stored at the National Air and Space MuseumNational Air and Space Museum
The National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world. It was established in 1976. Located in Washington, D.C., United States, it is a center for research into the history and science of aviation and...
in Washington, D.C.
Washington, D.C.
Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....
. It consists of one fuselage (minus powerplant) and a vertical stabilizer
Vertical stabilizer
The vertical stabilizers, vertical stabilisers, or fins, of aircraft, missiles or bombs are typically found on the aft end of the fuselage or body, and are intended to reduce aerodynamic side slip. It is analogical to a skeg on boats and ships.On aircraft, vertical stabilizers generally point upwards...
.