Nakajima G5N Redux

The IJAAF version of the G5N1 was to be the Nakajima Ki-68, and the IJAAF version of the G5N2 was to be the Kawasaki Ki-85.

 

The Nakajima G5N Shinzan originated due to the Imperial Japanese Navy's interest in developing a long-range attack bomber capable of carrying heavy loads of bombs or torpedoes a minimum distance of 3,000 nmi (5,600 km; 3,500 mi). To meet this requirement, it became apparent a four-engine lay-out would be necessary. As Japanese aircraft manufacturers lacked experience in building such large complex aircraft, the Navy was forced to search for a suitable existing foreign-made model upon which to base the new design. It settled on the American Douglas DC-4E airliner. In 1939 the sole prototype of this airliner (previously rejected by American airline companies) was purchased by Nippon Koku K.K. (Japan Airlines Co) and clandestinely handed over to the Nakajima Aircraft Company for dismantling and inspection.

The design that emerged from this study was for an all-metal mid-wing monoplane with fabric-covered control surfaces and powered by four 1,870 hp Nakajima NK7A Mamoru 11 air-cooled radial engines driving four-bladed propellers. Notable features included a long ventral bomb-bay, glazed nose and twin tailfins replacing the DC-4E's distinctive triple rudder. The DC-4E's retractable tricycle undercarriage was retained, as well as the original wing form and powerplant arrangement. Defensive armament comprised one 20mm Type 99 Model 1 cannon each in a power-operated dorsal and tail turret plus single-mount hand-operated 7.7mm Type 97 machine guns in the nose, ventral and beam positions.

The first prototype G5N1 made its maiden flight on 10 April 1941. Overall performance proved disappointingly poor however, due to a combination of excessive weight, the unreliablity of the Mamoru engines and the complexity of the design. Only three more prototypes were completed. In an attempt to salvage the project, two additional airframes were fitted with 1,530 hp Mitsubishi MK4B 12 "Kasei" engines and redesignated G5N2s. Although the Mitsubishi engines were more reliable than the original Mamoru 11s, the aircraft was now even more hopelessly underpowered and further development of the type was halted.

Operational history
Of the six completed Shinzans, four of them (two G5N2s and two G5N1s re-engined with the Kasei 12) were relegated for use as long-range Navy transports under the designation Shinzan-Kai Model 12 Transport G5N2-L. The Allies allocated the code-name "Liz" to the aircraft, in the expectation it would be used as a bomber.

Variants
    G5N1: Four-engined heavy bomber. Production version, four built.
    G5N2: Four Mitsubishi MK4B 12 "Kasei" radial engines in place of Nakajima Mamoru 11 engines. Two built.
    G5N2-L: Long-range Navy transport conversion.

Proposed Variants
    Nakajima Ki-68: Japanese Army heavy bomber. Four Mitsubishi Ha-101 or Nakajima Ha-103 engines.
    Kawanishi Ki-85: Japanese Army heavy bomber. Four Mitsubishi Ha-111M engines.

Hiro G2H

As the Washington (Disarmament) Treaty of 1922 limited the tonnage for capital ships for the US Navy, the Royal Navy and the Japanese Navy, so did the London (Disarmament) Treaty of 1930 limit the number of smaller ships including aircraft carriers and cruisers. Japanese Navy planners recognized the capability of Navy land-based bombers that could be used to supplement and reinforce fleet activities and thus were responsible for the development of the Hiro Navy Type 95 Land-based Attack Aircraft.

To meet this new requirement for air power starting in 1932, Rear Admiral Isoroku Yamamoto, Chief of Engineering Department, Naval Air Headquarters, called for a land-based long-range attack bomber that could fly more than 2,000nm and carry two tons of bombs. The Hiro Arsenal was selected for the project, for at that time it was the most experienced in the design of all-metal large aircraft. Chief designer was Lieut-Cdr (Ordnance) Jun Okamura who had served in this capacity for the preceding Type 91 Flying-boat project. This land-based bomber became the primary concern at the Hiro Arsenal, diverting attention from the development of the flying-boats previously described.

At the start of the project, the prototype's designation was the Hirosho 7-Shi Special Attack Aircraft, with the short designation G2HI. Structurally, it was a combination of a large wing of traditional Wagner diagonal tension-field structure and a slender fuselage of monocoque construction. The twin fins and rudders were similar to those of the final design of the Type 90-1 Flying-boats, and the ailerons were of the Junkers double-wing variety. One of the innovative features of the armament installation was a cylindrical belly gun turret which retracted into the fuselage. This feature was carried over into early versions of the Mitsubishi Navy Type 96 Land-based Attack Aircraft, that were code-named Nell by the Allies during the Pacific War.

To power the new bomber, two 900-1,180hp Type 94 water-cooled engines were selected, the most powerful aircraft engines available at that time. They were being developed by the Hiro Arsenal as a scaled-up version of the 600hp Type 90 Engine. It was felt that with these new engines, the aeroplane would be equivalent to a three- or four-engined aircraft of the time. Although the airframe dimension, wing area, and empty weight were almost identical to the Type 90-1 Flying-boat, aircraft range and payload were increased by nearly 50 percent. This was the largest land-based aeroplane in the Navy at that time, second only to the Army's Type 92 Heavy Bomber (Ki.20) of the Junkers-G 38 design, yet it was the first of such a large size to be designed from the beginning as a land-based attack bomber. With two engines, its wing span was 103 ft 11 1/4in, marginally bigger than the four-engined Boeing B-17 Flying Fortress with 103ft 9in wingspan.

The first prototype was completed on 29 April, 1933, at the Hiro Arsenal and moved by ship to Yokosuka. There it made its first flight in mid-May 1933 in the presence of Rear Admiral Yamamoto who had originated this bomber concept for the Navy. Making the first flight were Lieut-Cdr Shinnosuke Muneyuki and Lieut-Cdr Toshihiko Odahara, both of the Flight Experiment Group of the Yokosuka Kokutai. After taking off, Muneyuki made one pass over the field for the spectators and proceeded to Kasumigaura Air Base where testing was to take place.

As flight evaluations continued, it was found that the aeroplane possessed outstanding performance as the Navy's largest land-based aeroplane at that time. But shortcomings became evident, including tail vibrations caused by the light structure of the fuselage, aileron flutter, and unreliable engines. One aircraft was lost during test flying because of aileron and tail flutter, causing it to ditch in Tokyo Bay. Corrections were made to the design enough to justify production.

In June 1936, the aeroplane was officially accepted by the Navy as the Type 95 Land-based Attack Aircraft, at the same time as the Navy accepted the Type 96 Land-based Attack Aircraft (G3M 1), Nell. To avoid identity confusion between the two, the G3Ml was referred to as the Type 96 Chu-ko (Medium Attack) or simply 'Chuko,' while the G2H was called the Type 95 Dai-ko (Large Attack) or 'Dai-ko.'

After six of the G2H bombers had been produced at Hiro Arsenal, production was transferred to Mitsubishi. Before long, however, the Navy asked that production be concentrated on the smaller G3M, curtailing the G2H because of maintenance difficulties with the Type 94 Engines and the aeroplane's low-speed flying characteristics. Consequently, production ended with only two having been manufactured by Mitsubishi.

With the activation of the Kisarazu Kokutai on 1 April, 1936, all remaining G2H1s (a total of eight were built) were assigned to this unit but were regarded as second-line aircraft because of the better performance of the G3Ms.

Heavy losses were experienced by G3Ms over Nanjing in August 1937, resulting in the deployment of the G2Hs to an airfield on Saishuto Island (now Cheju Do, off the southern coast of South Korea), and while en route, and for unexplained reasons, one G2H dropped out of formation and crashed near the coast of Sagami Bay southwest of Tokyo. Once in place, and established as the 1st Combined Kokutai with other forces from Kanoya, they made their first mission into China in support of ground forces in the Shanghai area on 30 September, 1937, under the command of Lt Motokazu Mihara. They made further attacks against nine major combat areas and received considerable damage from AA fire but no aeroplanes were lost.

Disaster did catch up with these G2Hs on 24 October, 1937, when one aircraft caught fire while its engines were being started and soon exploded. The fire spread to the other G2Hs, each loaded with three 250kg, five 60kg and five 50kg bombs, exploding successively until four aircraft were destroyed and the fifth badly damaged.

Specifications (G2H1)
Twin-engined land-based mid-wing monoplane bomber. All-metal stressed skin construction.
Crew of seven.
Two 900-1, 180hp Hiro Type 94-1 eighteen-cylinder W-type water-cooled engines, driving four-bladed wooden propellers.
One nose-mounted flexible 7.7mm machine-gun, twin dorsal 7. 7mm machine-guns retractable turret-mounted, one retractable turret-mounted ventral 7.7mm machine-gun. Bomb load: six 250kg (551Ib) bombs or four 400kg (881Ib) bombs.
Span 31.68m (103ft 11 1/4in); length 20.15m (66ft 1 1/4in); height6.28m (20ft 7 1/4in); wing area 140sq m (1,506.996sq ft).
Empty weight 7,567kg (16,682Ib); loaded weight 11,000kg (24,250Ib); wing loading 78.5kg/sq m(16Ib/sq fr); powerloading 6.11 kg/hp (13.4lb/ hp).
Maximum speed 132kt (152mph) at 1,000m (3,280ft); cruising speed 90kt (104mph); climb to 3,000m (9 ,843ft) in 9min 30sec; service ceiling 5,130m (16,830ft); range 1,080 to 1,557nm (1,245 to 1,800sm).
Hirosho built six from 1933 and Mitsubishi built two from 1936.

Mitsubishi G4M Part II

Few would know it by its official designation, the Navy Type 1 Attack Bomber. The Allies called it the BETTY but to the men that flew the airplane, it was popularly, but unofficially, the 'Hamaki,' Japanese for cigar, in honour of the airplane's rotund, cigar-shaped fuselage. The Japanese built more of them than any other bomber during World War II. From the first day of war until after the surrender, BETTY bombers saw service throughout the Pacific and Indian Oceans. Like its stable mate, Mitsubishi's Zero Fighter the Hamaki soldiered on long after it became obsolete, even dangerous, to fly wherever Allied interceptors prowled.

In July 1937, the new Mitsubishi G3M bomber (Allied codename NELL) went into service in China. Only two months later, the Navy issued a specification to Mitsubishi for a NELL replacement. At that time, the requirements were unprecedented for a twin-engine, land-based attack bomber: flying at a top speed of 398 kph (247 mph) and an altitude of 3,000 m (9,845 ft), the new bomber had to fly a distance of 4,722 km (2,933 miles) without a torpedo or equivalent weight in bombs. When carrying an 800 kg (1,768 lb) torpedo or the same weight in bombs, the Navy needed the bomber to fly at least 3,700 km (2,300 mi).

To meet the requirements, a Mitsubishi design team led by Kiro Honjo crafted an airplane called the G4M with fuel tanks in the wings that were not resistant to explosion when punctured during combat. These tanks were much lighter in weight than explosion-proof (also called 'self-sealing') gas tanks. The decision not to incorporate the heavier, safer fuel tanks was necessary to meet the Navy's range requirements. Mitsubishi incorporated this same design feature in the Zero, for the same reasons and with the same results. Both aircraft had unprecedented range but they were also extremely vulnerable to the machine gun and cannon fire from Allied fighter aircraft. The BETTY was so prone to ignite that the Allies nicknamed it the 'flying lighter.'

The fuselage was streamlined but rotund to allow space for a bomb bay within the wing centre section and to allow the 7 to 9-man crew to move about. About half the crew were gunners who manned the defensive armament positions. Bomber crews flying the NELL were virtually incapable of defending themselves from concentrated fighter attacks, so Honjo paid special attention to this aspect of the G4M. He incorporated 7.7 mm (.30 cal.) guns in the nose, atop the mid-fuselage behind the cockpit, and on both sides of the fuselage behind the wing. In the tail, he introduced a 20 mm cannon. Although the G4M now had a more potent sting, Honjo again sacrificed crew protection to the Navy's demands for great range. He omitted armour plate.

The first G4M prototype left the factory in September 1939 and made the trek to Kagamigahara Airfield for Mitsubishi's Nagoya plant had no company airstrip. Kagamigahara was 48 km (30 miles) to the north. Japan's newest and most advanced bomber made the trip, disassembled and stacked on five ox-drawn farm carts, over unpaved roads! After arriving at the airfield, the first G4M was reassembled and flown by test pilot Katsuzo Shima on October 23, 1939. Initial results were impressive, but the Navy shelved the bomber for a time in favour of a variant to be called the G6M1. Navy leaders hoped that by increasing the number of defensive cannons, the G6M1 could become a heavy escort fighter for other bombers but this diversion failed to live up to expectations, and the Navy ordered the G4M1 into production. The U. S. Army Air Corps conducted a similar experiment using a modified Boeing B-17 bomber designated the B-40 but this idea too failed to survive operational testing and was soon abandoned. The first production G4M rolled off the line in April 1941. For the remainder of the war, the BETTY assembly line continued to run.

Operationally, BETTY crews achieved much in their first year of combat. They devastated Clark Field, Philippine Islands, on December 8, 1941, and participated in sinking the British battleships HMS "Prince of Wales" and HMS "Repulse" on December 10. They ranged across the length and breadth of the Pacific theatre, attacking targets from the Aleutians to Australia. Against limited fighter opposition, the lack of armour and self-sealing fuel tanks was no hindrance. The savings in airframe weight allowed the G4M to attack targets at unprecedented ranges. But as Allied fighter strength increased, the BETTY began to reveal its fatal vulnerabilities. Admiral Isoroku Yamamoto, architect of the Pearl Harbour attack, died on April 18, 1943, along with his entire staff when U. S. Army Air Corps P-38 Lightnings intercepted and destroyed the two BETTY bombers that carried them. Six escorting Zeros flew guard but in a matter of seconds, the Air Corps pilots shrugged off the escorting fighters and sent both BETTYs crashing down in flames.

As the war dragged, improved bombers failed to materialize so Mitsubishi fielded different versions of the G4M to fulfil new missions, and to eliminate the various weaknesses in the basic design. Front-line combat units operated many variants and sub-variants with different engines and armament packages. The G4M2 was a complete redesign but it did not overcome the airplane's vulnerability to Allied firepower. Mitsubishi tried again to reduce the bomber's tendency to burn. The firm changed the wing to a single-spar configuration and installed self-sealing fuel tanks with a capacity about one-third less than earlier versions. The capacity dropped because of the material inserted in the tank to block leaking fuel when gunfire perforated the tank. Armour plate was also added to all crew positions and the tail turret was redesigned. As a result of these modifications, the fuselage was shortened and the centre-of-gravity shifted forward. To re-balance the bomber, dihedral was added to the horizontal stabilizer. This version was called the G4M Model 34.

VERSIONS
An early-production Mitsubishi G4M1 Model 11 without the propeller spinners

G4M1
G4M1 Prototypes
    Japanese Navy land Based Bomber Type 1. Two prototypes built.
G4M1 Model 11
    Japanese Navy Land Attack Bomber Type 1. The first bomber model of series, with 1,140 kW (1,530 hp) Mitsubishi MK4A Kasei Model 11 engines driving three-blade propellers. Following modifications were made during the production:
    March 1942: The first aircraft (241st production example) fitted with MK4E Kasei Model 15 engines with larger superchargers for better high altitude performance, became standard in August 1942 from 406th aircraft onwards. These MK4E-engined aircraft have often (erroneously) been referred as the G4M1 Model 12.
    Summer 1942: Propeller spinners introduced.
    March 1943: From 663rd machine onwards, 30 mm (1.18 in) rubber ply sheets installed beneath the wing outer surfaces to protect the undersides of the fuel tanks (speed reduced by 9 km/h/6 mph and range by 315 km/196 mi), 5 mm (.2 in) armour plates added into tail gunner's compartment.
    Spring 1943: Outer half of the tail cone cut away in order to improve tail gunner's field of fire.
    August 1943: A completely redesigned tail cone, with reduced framing and wide V-shaped cut out; this form of tail cone was also used in all G4M2 models.
    September 1943: Individual exhaust stacks from 954th airframe onwards.
Production of the G4M1 ended in January 1944.

G4M2
The first of the four G4M2 prototypes flew in December 1942. It differed from the preceding model in having MK4P Kasei Model 21 engines with VDM Electric four-blade propellers capable of full feathering function, redesigned main wings with LB type laminar flow airfoil,  and widened tail horizontal stabilizer wing area, which improved service ceiling to 8,950 m (29,360 ft) and maximum speed to 437 km/h (236 kn, 272 mph). Main wing fuel tanks were enlarged to 6,490 L (1,715 US gal) which increased the range to 6,100 km (3,790 mi/ 3,294 nmi overloaded, one way). An electrically powered dorsal turret featuring a 20 mm cannon was introduced in place of G4M1's dorsal position with a 7.7 mm machine gun, total guns armed were 2 × 20 mm Type 99 cannon (1 × tail turret, 1 × top turret), 4 × 7.7 mm Type 92 machine gun (1 × nose, 2 × waist, 1 × cockpit side). External differences also included increased nose glazing, flush side gun positions instead of blisters, and rounded tips of wings and tail surfaces. These major improvements also made it possible for the G4M2 to carry more powerful bombs; 1 × 1,055 kg (2,326 lb) Type 91 Kai-7 (improved model 7) aerial torpedo or 1 × 800 kg (1,760 lb) bomb or 2 × 500 kg (1,100 lb) bombs or one Type 3 – 800 kg (1,760 lb) no.31 ray-detective type bomb + 12 × 60 kg (130 lb) bombs. This model, G4M2, was put into service in mid-1943.
G4M2 Model 22
    The base model, the first production example completed in July 1943. Introduced bulged bomb bay doors from 65th aircraft onwards, and an optically flat panel in the nose cone from the 105th aircraft onwards.
G4M2 Model 22Ko
    Very similar to previous model. Carried Type 3 Ku Mark 6 search radar and was armed with two 20 mm Type 99 Mark 1 cannons replacing the 7.7 mm machine guns in the lateral positions.
G4M2 Model 22 Otsu
    Dorsal turret cannon changed to longer-barreled 20 mm Type 99 Mark 2.
G4M2a Model 24
    Modified Model 22, MK4T Kasei 25 1,340 kW (1,800 hp) engines, with bulged bomb bay doors as standard for larger bomb capacity. Externally distinguishable from the Model 22 by a carburetor air intake on the top of the engine cowling.
G4M2a Model 24 Ko/Otsu
    Armament similar to Model 22 Ko/Otsu respectively.
G4M2a Model 24 Hei
    Modified 24 Otsu, with one 13.2 mm (.51 in) Type 2 machine gun mounted in tip of the nose cone, radar antenna relocated from that position to above the nose cone.
G4M2b Model 25
    One G4M2a modified to MK4T-B Kasei 25 Otsu 1,360 kW (1,825 hp) engines. Only experimental.
G4M2c Model 26
    Two G4M2a modified to MK4T-B Ru Kasei 25b 1,360 kW (1,825 hp) engines with turbochargers.
G4M2d Model 27
    One G4M2 modified to MK4V Kasei 27 1,340 kW (1,800 hp) engines.
G4M2e Model 24 Tei
    Special version for the transport of the ramming attack bomb plane Kugisho/Yokosuka MXY-7 Ohka ("Baka") Model 11, conversions of G4M2a Models 24 Otsu and 24 Hei. Had armour protection for the pilots and fuselage fuel tanks.
MXY11 Yokosuka Navy Type 1 Attack Bomber
    Ground Decoy Non-flying replica of Mitsubishi G4M2 developed by Yokosuka

G4M3
G4M3 Model 34
    Redesigned G4M2 with added self-sealing fuel tanks, improved armor protection and an entirely new tail gunner's compartment similar to that of late model B-26 Marauders. Wings were also redesigned and the horizontal tailplane was given dihedral. Armed with 2 × 7.7 mm Type 92 machine guns in nose cabin and in both side positions, and 1 × 20 mm Type 99 Model 1 cannon in dorsal turret and tail. Entered production in October 1944 in G4M3a Model 34 Ko form with 20 mm cannon in side positions instead of machine guns.
G4M3a Model 34 Otsu and Hei
    Similar modifications as in corresponding Model 24 variants.
G4M3 Model 36
    Prototype. Two G4M2 Model 34 modified to Mitsubishi MK4-T Kasei 25b Ru 1,360 kW (1,825 hp) engines.

G6M1
G6M1 Japanese Navy Long Range Heavy Fighter Type 1
    Initial model of the series, armed with 20 mm Type 99 cannons between each side of fuselage and in tail, 1 × 7.7 mm machine gun in nose cabin and 1 × 30 mm cannon in front ventral position; 30 built.
G6M1-K Trainer, Japanese Navy Type 1
    Converted G6M1s.
G6M1-L2 Transport Type 1, Japanese Navy
    Modified as transports.

Mitsubishi G4M Part I

 

The bulbous G4M was the most numerous and best-known Japanese medium bomber of World War II. It possessed incredible range, but its unarmored fuel tanks led to the unenviable nickname “Flying Lighter.”

In 1937 the Imperial Japanese Navy issued an incredibly difficult specification mandating production of land-based bombers with even greater range than the superb G3M. Although such performance was usually attained by four-engine designs, the new craft was restricted to only two. That year Kiro Honjo commenced work on a machine whereby fuel capacity was emphasized to the exclusion of all other considerations. In 1939 the G4M prototype was flown as an all-metal, midwing design with rakish wings and tail surfaces melded to a rotund fuselage. As expected, the airplane performed well and possessed impressive range. However, this was achieved by stuffing as much fuel as possible into wing tanks that remained unarmored to save weight; crew armor was also deleted for the same reason. Nonetheless, the navy was highly pleased with the G4M, and in 1940 it entered production. The following year they were baptized under fire in northern China, performing well against limited opposition. When the Pacific war broke out in December 1941, roughly 160 G4Ms were in service. Allied forces gave them the code name Betty.

The G4M came as quite a surprise to British and American forces, who believed themselves beyond the reach of medium bombers. But in quick succession, G4Ms helped sink the battleships HMS Repulse and Prince of Wales, and they plastered airfields throughout the Philippines. It was not until the spring of 1942 that the Betty’s weakness was revealed. The very attributes endowing it with such long range caused it be destroyed by a few tracer rounds. The G4Ms took staggering losses during the Guadalcanal campaign, and the Japanese finally introduced self-sealing tanks and crew armor in subsequent versions. One of the last roles of the G4M would be to carry the Yokosuka MXY 7 Oka suicide rocket. Production totaled 2,416 of all versions.

Production
G4M1 Model 11: 1172 examples (including prototypes.)
G4M2 Models 22, 22 Ko and 22 Otsu: 429 examples.
G4M2a, Models 24, 24 Ko, 24 Otsu, 24 Hei, and 24 Tei: 713 examples.
G4M3 Models 34 Ko, 34 Otsu, and 34 Hei: 91 examples.
G6M1: 30 examples.
Total production of all versions: 2,435 examples.

Specifications (G4M1, Model 11)
General characteristics
    Crew: 7 (main-pilot, co-pilot, navigator/bombardier/nose gunner, captain/top turret gunner, radio operator/waist gunner, engine mechanic/waist gunner, tail gunner)
    Length: 19.97 m (65 ft 6¼ in)
    Wingspan: 24.89 m (81 ft 7¾ in)
    Height: 4.9 m (16 ft 1 in (in a horizontal position))
    Wing area: 78.13 m² (840.9 ft²)
    Airfoil: Mitsubishi type
    Empty weight: 6,741 kg (14,860 lb)
    Loaded weight: 9,500 kg (20,944 lb)
    Max. takeoff weight: 12,860 kg (28,350 lb)
    Powerplant: 2 × Mitsubishi MK4A-11 "Kasei" (Fire star) 14 cylinder radial engines, 1,141 kW (1,530 hp) each
    Propellers: 4-bladed Hamilton Standard licensed Sumitomo constant speed variable-pitch
Performance
    Maximum speed: 428 km/h (230 kn, 265 mph)
    Cruise speed: 315 km/h (175 kn, 196 mph)
    Stall speed: 120 km (75 mph)
    Range: 2,852 km, one way (1,540 nmi, 1,771 mi, one way (overloaded: 5,040 km (2721 nmi, 3,132 mi)))
    Service ceiling: 8,500 m (27,890 ft)
    Rate of climb: 550 m/min (1,800 ft/min)
Armament
    Guns: 1× 20 mm Type 99 cannon (tail turret), 4× 7.7 mm Type 92 machine gun (nose turret ×1, waist positions ×2, top turret ×1)
    Bombs: 1× 858 kg (1,892 lb) Type 91 Kai-3 (improved model 3) aerial torpedo or 1× 800 kg (1,764 lb) bomb or 4× 250 kg (551 lb) bombs

Tachikawa Ki-74

Although first conceived as early as 1939, the Tachikawa Ki-74 had not been placed in full production when the Pacific war ended. During those six years its intended role had been changed from that of long-range reconnaissance to that of long-range stratospheric bombing.

Under the guidance of Dr Kimura, the Ki-74 was originally designed in the spring of 1939 to meet the requirements of a specification issued by the Koku Hombu and calling for a long-range reconnaissance aircraft capable of operating west of Lake Baikal from Manchurian bases. The aircraft was to have a range of 5,000 km (3,107 miles) at a cruising speed of at least 450 km/h (280 mph). To meet these performance requirements, Dr Kimura proposed using a pair of 2,400 hp Mitsubishi Ha-214M radials driving six-blade propellers. and fitting a pressure cabin. However, pending development of the pressure cabin system tested on the Tachikawa SS-1 and A-26/Ki-77, the project was temporarily suspended.

Late in 1941 the project was revived as a long-range high-altitude bomber-reconnaissance aircraft capable of bombing the United States mainland. To fit the aircraft for its new role, Tachikawa added bombing equipment, self-sealing fuel tanks and armour to the original design and decided to replace the Ha-214M engines with a pair of Mitsubishi Ha-211-I radials, rated at 2,200 hp for take-off, 2,070 hp at 1,000 m (3,280 ft) and 1,720 hp at 9,500 m (31,170 ft). The design of the aircraft was approved by the Koku Hombu in September 1942 and construction of three prototypes was authorised. The first prototype, completed in March 1944, was followed by two externally identical aircraft which were powered by a pair of turbosupercharged Ha-211-I Ru radials, rated at 2,200 hp for take-off, 2,070 hp at 1,000 m (3,280 ft) and 1,720 hp at 9,500 m (31,170 ft). However, during the flight trial programme both versions of the Mitsubishi Ha-211 suffered from teething troubles and it was decided to replace them on the pre-production aircraft with the lower-powered but more reliable turbosupercharged Mitsubishi Ha-104 Ru radials, rated at 2,000 hp for take-off, 1,900 hp at 2,000 m (6,560 ft) and 1,750 hp at 6,000 m (19,685 ft).

Thirteen Ha-104 Ru powered pre-production aircraft were built and were still undergoing tests when the war ended. All five crew members were seated in a pressure cabin in the forward fuselage, and the aircraft was armed with a single remotely-controlled 12.7 mm (0.5 in) machine-gun in the tail and carried a bomb-load of 1,000 kg (2,205 lb). Plans were made to use the Ki-74s in bombing attacks against B-29 bases at Saipan as soon as sufficient aircraft were available, but the Japanese surrender terminated the project. Although the Ki-74 was never encountered during the war, the Allies were aware of its development, but thinking at first that it was a 'super-range, high-speed fighter' intended for long-range escort duty they accordingly assigned to it a male name: 'Pat'; when the true role of the aircraft was discovered the code-name was changed to 'Patsy'.

The fourth pre-production aircraft (Ki-74 c/n 7) was modified in 1944 to undertake non-stop flights between Japan and Germany, but the Third Reich capitulated before the first of these flights could be made. Other developments included a pure bomber version, the Ki-74-II with the bomb-load increased to 2,000 kg (4,410 lb), and a transport version, but both these projects were abandoned before completion.


Technical Data

Manufacturer: Tachikawa Hikoki KK (Tachikawa Aeroplane Co Ltd).
Type: Twin-engined high-altitude long-range reconnaissance-bomber.
Crew (5): Enclosed in pressure cabin.
Powerplant: (1st prototype) Two Mitsubishi Ha-211-I eighteen-cylinder air-cooled radial engine, driving four-blade metal propellers, (2nd and 3rd prototypes) two Mitsubishi Ha-221-I Ru eighteen-cylinder air-cooled radial engines, driving four-blade metal propellers, (4th-16th aircraft) two Mitsubishi Ha-104 eighteen-cylinder air-cooled radial engines, driving four-blade metal propellers.
Armament: One remotely-controlled 12.7 mm (0.5 in) Type 1 (Ho-103) machine-gun. Bomb-load: 1,000 kg (2,205 lb).
Dimensions: Span 27 m (88 ft 7 in); length 17.65 m (57 ft 10 7/8 in); height 5.1 m (16 ft 8 25/32 in); wing area 80 sq m (861.11 sq ft).
weights: Empty 10,200 kg (22,487 lb); loaded 19,400 kg (42,770 lb); wing loading 242.5 kg/sq m ( 49.7 lb/sq ft); power loading 4.4 kg/hp (9.7 lb/hp).
Performance: maximum speed 570 km/h (354 mph) at 8,500 m (27,890 ft) cruising speed 400 km/h (249 mph) at 8,000 m (26,245 ft); climb to 8,000 m (26,245 ft) in 17 min; service ceiling 12,000 m (39,370 ft); range 8,000 km (4,971 miles).
Production: A total of 16 Ki-74s were built by Tachikawa Hikoki KK between march 1944 and August 1945.

Mitsubishi Ki-109

The Mitsubishi Ki-109 with nose-mounted 75 mm Type 88 cannon.

 

Early in the war when Japanese fighter pilots were in control of the skies, the few Boeing B-17 Flying Fortresses available in the Southwest Pacific area were the only Allied aircraft to challenge their superiority effectively. As the war developed in favour of the Allies, the longer-ranging Consolidated B-24 Liberators, better suited to the island-hopping war, replaced the B-17s. But for the Japanese the problem of attempting to destroy high flying, well protected and formidably armed bombers remained the same. The Koku Hombu were also aware of the US development of a still more formidable four-engined bomber, the Boeing B-29 Superfortress, and by 1943 they were feverishly studying every means of defence against this feared enemy aircraft.

In early 1943 the Mitsubishi Ki-67 heavy bomber then undergoing flight trials had proved that despite its size and weight it was fast and remarkably manoeuvrable. Consequently in November 1943, officers of the Rikugun Kokugijutsu Kenkyujo (Army Aerotechnical Research Institute) at Tachikawa suggested that the Ki-67 be used as the basis for a hunter-killer aircraft. The project received the designation Ki-109 and two versions were to be built: the Ki-109a, the killer was to mount in the rear fuselage two obliquely-firing 37 mm (1.46 in) Ho-203 cannon while the Ki-109b, the hunter, was to be equipped with radar and a 400 mm searchlight. However, soon thereafter, the project was re-directed at the instigation of Maj Sakamoto who suggested that a standard 75 mm (2.95 in) Type 88 anti-aircraft cannon be mounted in the nose of a standard Ki-67. It was hoped that with this large cannon the aircraft would be able to fire on the B-29s while staying well out of range of their defensive armament. As the Koku Hombu anticipated that, initially at least, B-29s would have to operated without fighter escort, the project was found sound and feasible and, accordingly, Mitsubishi were instructed in January 1944 to begin designing the aircraft, which retained the Ki-109 designation.

Modification of the Ki-67 to mount a 75 mm (2.95 in) Type 88 (Ho-401) cannon in the nose was entrusted to a team led by Engineer Ozawa and the first prototype was completed in August 1944, two months after the B-29s had made their first bombing raid over Japan. Except for its nose, in the lower part of which was mounted the Type 88 (Ho-401) cannon, the Ki-109 prototype was identical to the Ki-67 and retained the waist gun positions and dorsal and tail turrets of the bomber. Ground and inflight test firings of the heavy gun were affected by Maj Makiura of the Rikugun Kokugijutsu Kenkyujo and was sufficiently successful to warrant the placing of an initial order for 44 aircraft. The first twenty-four were each to be powered by two Mitsubishi Ha-104 radials rated at 1,900 hp for take-off, 1,810 hp at 2,200 m (7,220 ft) and 1,610 hp at 6,00 m (20,015 ft) but subsequent aircraft were to receive a pair of Mitsubishi Ha-104 Ru radials fitted with Ru-3 exhaust-driven turbosuperchargers and rated at 1,900 hp for take-off and 1,810 hp at 7,360 m (24,150 ft) to improve performance at the cruising altitude of the B-29s. These engines were actually tested on the second Ki-109 prototype, but no production aircraft were powered by Ha-104 Ru engines. Another attempt to im prove climbing speed was made when a solid propellent rocket battery was installed in the rear bomb-bay of the first prototype but this scheme was abandoned.

Starting with the third Ki-109, the dorsal turret and lateral blisters were dispensed with and no bomb-bay fitted. Fifteen shells were carried for the 75 mm (2.95 in) Type 88 cannon which was hand-loaded by the co-pilot, and the sole defensive armament consisted of a flexible 12.7 mm (0.5 in) Type 1 machine-gun in the tail turret. The rest of the airframe and the powerplant were identical to those of the Ki-67. Despite the lack of high-altitude performance the Ki-109 was pressed into service with the 107th Sentai but, by the time enough aircraft were on hand, the B-29s had switched to low-altitude night operations.

Unit Allocated
107th Sentai.

Technical Data
Manufacturer: Mitsubishi Jukogyo KK (Mitsubishi Heavy Industries Co Ltd).
Type: Twin-engined heavy interceptor.
Crew (4): Pilot, co-pilot and radio-operator in forward cabin and gunner in rear turret.
Powerplant: Two Army Type 4 (Mitsubishi Ha-104) eighteen-cylinder air-cooled radial engines. driving four-blade constant-speed metal propellers.
Armament: One forward-firing 75 mm (2.95 in) Type 88 cannon and flexible one 12.7 mm (0.5 in) Type 1 machine-gun in the tail turret.
Dimensions: Span 22.5 m (73 ft 9 13/16 in); length 17.95 m ( 58 ft 10 11/16 in); height 5.8 m (19 ft 1 1/32 in); wing area 63.85 sq m (708.801 sq ft).
Weights: Empty 7,424 kg (16,367 lb); loaded 10,800 kg (23,810 lb); wing loading 164 kg/sq m (33.6 lb/sq ft); power loading 2.8 kg/hp (6.3 lb/hp).
Performance: Maximum speed 550 km/h (342 mph) at 6,090 m (19,980 ft); range 2,200 km (1,367 miles).
Production: A total of 22 Ki-109s were built by Mitsubishi Jukogyo KK between August 1944 and March 1945.

Mitsubishi B2M1 and 2 Navy Type 89 Carrier Attack Aircraft - Part 2

For reconnaissance duties the crew consisted of pilot, wireless operator/bomb-aimer and observer/gunner sitting in three separate cockpits and placed close together for ease of intercommunication, either verbally or by hand-written notes. An aperture in the floor of the centre cockpit served the dual-purpose of course-setting bomb-sight mounting and optional fourth gun position, the Lewis being carried on rails in the floor and stowed under it when not in use. For torpedo-carrying the crew was reduced to two and the fuel to 454 litres (100 Imp gal).

The prototype Blackburn T.7B, or 3MR4, was completed at the end of November 1929 and first flown at Brough without markings by A M Blake on 28 December 1929 that year. Test flights were made with and without torpedo but no time was lost, for records show that it was packed form shipment to Japan on 3 January 1930, arriving there the following month. Accompanying the aircraft was its chief British designer, G E Petty and a Blackburn working party, who were to assemble the aircraft on arrival and to supervise the building of additional aircraft.

On arrival it was painted up with the Japanese Rising Sun disc insignia and closely examined by Mitsubishi engineers who immediately began tooling-up the factory and making ready for production. There examination was, if anything too searching, for the handle of the starting magneto was placed in the cockpit in such a position that it could not rotate (and therefore the engine could not start), unless the main oil cock was turned on; failing to see the wisdom of this arrangement, the Japanese repositioned the handle without reference to the designer, with the inevitable result that one of their pilots took-off without turning on the main oil supply and the aircraft crashed upside down in a paddy field when the engine seized. A second prototype, completed on 31 October, 1930, was powered by a 650 hp Mitsubishi Type Hi engine, but was lost due to a pilot error. The third prototype, completed on 2 February, 1931, was delivered to the Navy but suffered from shortcomings, such as engine oil overheating, difficulty in making a three-point landing which is so essential for carrier operations, and poor stability. The fourth prototype, with modifications to overcome the failings of its predecessors, performed well and was officially accepted as the Navy Type 89-1 Model 1 Carrier Attack Aircraft (short designation B2M1) in March 1932 and put into production. Unlike those of Blackburn's prototype, the fin and rudder were a rounded shape and the elevator horn balances were reduced in size. The nose was made slimmer by deleting the shuttered chin compartment and fitting a retractable radiator, and the tailplanes of late production machines had rounded ends and unbalanced elevators.

As the new aircraft entered service, engine problems and other shortcomings were discovered and frequently encountered during this transitional period. In addition, it was said to have had poor performance and poor operating cost. To correct these deficiencies, engineers Ohgi and Masufuji made changes in the materials used and manufacturing technique. As a result, this aircraft became the Navy Type 89-2 Carrier Attack Aircraft (B2M2), which remained in production until 1935. This variant of the Type 89 was armed with two instead of four machine-guns and able to carry 800 kg (1,764 lb) of bombs over short distances. This aircraft also featured wings of reduced span, a triangular fin and rudder and an even slimmer nose. Even allowing for 50 per cent greater tankage, both variants came out much overweight compared with the Blackburn T.7B.

In spite of high expectations for the new aircraft as a replacement for the Mitsubishi Type 13 Carrier Attack Aircraft, the Type 89 had a bad reputation with operational units even after the improvements which resulted in the Type 89-2. However, with the structure of steel and aluminium, the excellent characteristics of the Blackburn B-9 aerofoil, and use of Handley Page slots were valuable for future designs.

Although total production of the B2M1 and B2M2 amounted to 205 aircraft, it is said not to have been a worthwhile undertaking by Mitsubishi, who found the new constructional techniques very costly, compared with the machine's wooden predecessor, and the manufacturing licence for the Handley Page slots expensive. In addition, the unreliability of Japanese-built engines is believed to have led to a number of fatal accidents. Both variants served aboard the carriers Ryujo, Akagi and Kaga from 1933 until the Sino-Japanese war of 1937. Small numbers of Type 89 Attack Aircraft participated in campaigns during the Shanghai Incident, as did earlier Type 13 Carrier Attack Aircraft. Others were operational on the Japanese mainland with the Tateyama Air Corps and as carrier trainers with Omura Air Corps. Some of the Type 89s were donated to the Navy through the Hokoku-go programme, and, later the Type 89 design was released by the Navy as a civilian conversion, the Mitsubishi Type 89 General Purpose Aircraft.

Technical Data

Manufacturer: (1st prototype) Blackburn Aeroplane and Motor Car Co Ltd,
Mitsubishi Kokuki KK (Mitsubishi Aircraft Co Ltd).
Type: Single-engined carrier-borne attack aircraft.
Crew (2-3): (Reconnaissance) Pilot, wireless operator/bomb-aimer and observer/gunner or (torpedo-bomber) pilot and observer/gunner in tandem open cockpits.
Powerplant: One 650 hp Mitsubishi-built Type Hi (Hispano Suiza) twelve-cylinder vee water-cooled engine, driving a two-blade wooden propeller.
Armament: One (B2M1) fixed forward-firing 7.7 mm (0.303 in) Vickers machine-gun fitted along the port side of the fuselage, one flexible twin-mounted 7.7 mm (0,303 in) Lewis machine-guns on a double rotating mounting over the observer's cockpit, and optional 7.7 mm (0.303 in) Lewis machine-gun firing from ventral aperture in the floor of the central cockpit, (B2M2) one fixed forward-firing 7.7 mm (0.303 in) machine-gun and one flexible mounted 7.7 mm (0.303 in) machine-gun in observer's cockpit. Bomb load: One 907 kg (2,000 lb) Type 90 or Type 94 torpedo or two 113 kg (250 lb) bombs, or (B2M2) one 800 kg (1,764 lb) bomb.
Dimensions: Span (B2M1) 15.22 m (49 ft 11 1/4 in), (B2M2) 14.98 m (49 ft 1 3/4 in); length (B2M1) 10.27 m (33 ft 8 1/2 in), (B2M2) 10.18 m (33 ft 4 3/4 in); height (B2M1) 3.712 m (12 ft 2 in), (B2M2) 3.60 m (11 ft 9 1/2 in); wing area (B2M1) 55 sq m (592.034 sq ft), (B2M2) 49 sq m (527.448 sq ft).
Weights: Empty (B2M1) 2,260 kg (4,982 lb), (B2M2) 2,180 kg (4,806 lb); loaded 3,600 kg (7,936 lb); wing loading (B2M1) 65.5 kg/sq m (13.34 lb/sq ft), (B2M2) 73.5 kg/sq m (15 lb/sq ft); power loading (B2M1)4.87 kg/hp (10.7 lb/hp), (B2M2) 4.55 kg/hp (10 lb/hp).
Performance: Maximum speed (B2M1) 115 kt (132 mph), (B2M2) 123 kt (142 mph); climb to 3,000 m (9,843 ft) in (B2M1) 18 min, (B2M2) 12 min; range (B2M1) 960 nm (1,105 miles), (B2M2) 950 nm (1,094 miles).
Production: A total of 205 Type 89 aircraft (including 3 prototypes) were built by Mitsubishi Kokuki KK between October 1930 and 1935.

Mitsubishi B2M1 and 2 Navy Type 89 Carrier Attack Aircraft - Part 1

Running-up the Hispano-Suiza engine of the Blackburn T.7B in the presence of Mitsubishi representatives, Brough, December 1929.

The Blackburn-built 3MR4 prototype in Japan with Japanese Navy markings and two 113.3 kg (250 lb) bombs between the undercarriage legs.

In a competition that began in February 1928, the Navy asked for proposals from Aichi, Kawanishi, Mitsubishi and Nakajima for a design for a new carrier attack bomber to replace the Mitsubishi Type 13 Carrier Attack Aircraft, (BIM3). The Navy stipulated a crew of three, the 600 hp Hispano-Suiza, 450-600 hp BMW or the 600-650 hp Lorraine engine and that the structure was to be of mixed wood and metal construction. The span was to be less than 15 m (49.2 ft), length less than 10 m (33 ft), and height less than 3.8 m (12.4 ft).

Performance asked for was reasonable for that time, with a maximum speed of more than 110 kt (126.5 mph) at sea level, climb to 3,000 m (9,843 ft) in 15 minutes, and a ceiling of over 6,000 m (19,685 ft). Endurance was to be more than three hours with a load of bombs, or more than eight hours without bombs. The deck landing speed was to be less than 45 kt (52 mph), and take-off distance less than 45 m (148 ft) with a surface wind of 20 kt (23 mph).

Mitsubishi sub-contracted each different design study to three different teams. The first design termed 3MR3 was engineered by Herbert Smith, who had returned to England in June 1924. Mitsubishi decided to use an even newer engine, the 650 hp Armstrong Siddeley leopard. The company sub-contracted a second design study termed 3MR4 to the Blackburn Company in Britain, powered by the 600 hp Hispano-suiza. The third design study, the 3MR5, was sub-contracted to Handley Page Company, also in Britain. This was to have a 600 hp Hispano-Suiza engine like that of the 3MR4. Of the three design proposals, Mitsubishi selected the Blackburn-designed 3MR4 as the best and submitted it for the competition. The Navy declared this aircraft to be the design winner in December 1928, and Mitsubishi therefore directed Blackburn to manufacture the first prototype.

Before the order was placed, Mitsubishi sent engineer Hajime Matsuhara to England to gain technical knowledge on aircraft engineering planning and design, three additional engineers, Arkawa, Yui and Fukui, were also sent to Blackburn to learn the fundamentals that were to be incorporated into the 3MR4.

The Blackburn T.7B (or 3MR4), was a two-bay staggered biplane with Frise ailerons on all four wings and equipped with Handley Page leading edge slots, but the lower mainplane was some 0.33 m (13 in) greater in span than the upper and the outer interplane struts were not parallel to the inner. The fabric-covered all-metal wing structure followed standard Blackburn practice, using high-grade steel box spars built up from specially rolled and drawn sections in conjunction with duralumin ribs, the outer panels being hinged to the centre section rear spars. They folded with the aid of a jury strut, but the lower centre section, being of greater span than the upper, imparted some 45 degrees of tilt to them when folded.

The fuselage was of the usual Blackburn three-piece weldless steel-tube construction faired by aluminium panels to a point aft of the cockpit for ease of servicing and re-arming. The fabric-covered rear section was filled with flotation bags except for the stern bay, which housed the ballast weights used for C G adjustment when changing from three to two-crew operation.

Although larger, the divided oleo-sprung undercarriage and rectangular tail unit were similar in design and construction to those of the Beagle, and the tailplane was adjustable in the air by means of a handwheel on the starboard side of the cockpit. The tail skid was oleo-pneumatically sprung from the sternpost, and attachment points for a float undercarriage were an integral part of the fuselage structure although floats were in fact, never fitted.

The closely-cowled 600 hp Hispano-Suiza 51-12Lb twelve-cylinder vee water-cooled engine drove a two-blade wooden propeller and was mounted on duralumin bearers supported on a steel-tube structure, but for simplicity the old Swift/Dart/Velos cooling system was revived using a radiator compartment under the engine but with vertical instead of horizontal shutters. Total fuel capacity was 918.3 litres (202 Imp gal) housed in two 168.2 litres (37 Imp gal) gravity tanks in the top centre section, a 200 litres (44 Imp gal) tank between the pilot and the fireproof bulkhead, and a fourth of (84 Imp gal) capacity below the pilot's floor. For long-range operation a 386.4 litres (85 Imp gal) streamlined overload tank with nose-mounted, wind-driven fuel pump, could be carried in the torpedo crutches. A 41 litres (9 Imp gal) oil tank was fitted under the decking ahead of the pilot and the coolant header tank was in the centre section as on the Ripon.

Nakajima B6N Tenzan

In 1939 the Imperial Japanese Navy drew up its specification for a carrier-based torpedo-bomber to supersede the Nakajima B5N. The specifications issued by the navy called for very modern characteristics. A maximum speed of 288 mph (463 km/h), a cruising speed of 230 mph (370 km/h) and a range of 1,000 nautical miles (3335 km) without a bombload. To meet the requirement, Nakajima decided to use an airframe very similar to that of the earlier aircraft, differing primarily in its vertical tail surfaces. The navy had specified use of the Mitsubishi Kasei radial engine, but Nakajima decided to use instead its own 1,870 hp (1395 kW) Nakajima NK7A Mamoru 11 radial engine of similar output driving a four bladed Hamilton type propeller. The first of two prototypes was flown in spring 1941, but initial flight testing revealed a number of problems, including engine vibration and overheating, but the most serious was that of directional stability, requiring revised vertical tail surfaces. Final flight testing carried out aboard the aircraft carriers Ryuho and Zuikaku in the end of 1942, revealed further problems with the tuning of the engine and the need to reinforce the arrester hook and landing gear. It was not until February 1943 that the type entered production as the Navy Carrier Attack Bomber Tenzan Model 11, company designation Nakajima B6N1, incorporating a number of refinements as a result of extended flight testing. However, after only 135 production Tenzan (heavenly mountain) aircraft had been delivered a new crisis arose when Nakajima was ordered to terminate manufacture of the Mamoru engine, and use the more reliable 1,850 hp (1380 kW) Mitsubishi MK4T Kasei 25 engine, a step also taken to allow greater emphasis to be placed on production of the widely-used Nakajima Homare and Sakae engines.

The company was now compelled to use the engine which the navy had specified originally, the Mitsubishi Kasei, but fortunately the adaptation of the B6N airframe to accept this powerplant presented no major difficulties. The resulting aircraft, which was also the major production version, had the designation B6N2 and differed only from the B6N1 by the installation of the Mitsubishi Kasei 25 engine. The B6N2a variant had the rear-firing 7.7 mm (0.303 in) machine-gun replaced by one of 13 mm (0.51 in) calibre. When production ended, Nakajima had built a total of 1,268 B6Ns of all versions, this number including two modified B6N2 airframes which had served as prototypes for a proposed land-based B6N3 Model 13. The powerplant had been the improved 1,850 hp (1380 kW) Mitsubishi MK4T-C 25C version of the Kasei engine and the strengthened landing gear had larger wheels for operation from unprepared runways, but production did not start before the war ended. Allocated the Allied codename 'Jill', the B6Ns saw intensive use during the last two years of the war for conventional carrier operations and, in the latter stages, in kamikaze roles.

Variants

Nakajima B6N2 - Nakajima was ordered to cease using the Mamoru engine and use instead the Mitsubishi Kasei 25 engine, thus resulting in the redesignated B6N2. Although the Kasei 25 was slightly less powerful, this was offset by introducing a less drag version of the exhaust ports which also gave a slight jet-thrust like boost effect.

Nakajima B6N2a - This type differed from the B6N2 only by having a rear firing machine gun of 13 mm (0.51 in) calibre, instead of the 7.7 mm (0.303 in) type used on the B6N2.

Nakajima B6N3 - Two conversions of the B6N2a resulted in the B6N3 prototypes equipped with 1,850 hp (1380 kW) Mitsubishi MK4T-C Kasei 25C engines for evaluation as land based bombers.

(Navy Carrier Attack Bomber Tenzan "Heavenly Mountain" Model 11 - Nakajima B6N2)

Allied Codename: Jill

Type: Three Seat Carried based Torpedo Bomber

Design: Nakajima Hikoki KK with Kenichi Matsamura as led Technical Director

Manufacturer: Nakajima Hikoki KK

Powerplant: (B6N1) One 1,870 hp (1395 kW) Nakajima NK7A Mamoru 11 14-cylinder radial engine. (B6N2) One 1,850 hp (1380 kW) Mitsubishi MK4T Kasei 25 14-cylinder radial engine. (B6N3) One 1,850 hp (1380 kW) Mitsubishi MK4T-C Kasei 25C 14-cylinder radial engine.

Performance: Maximum speed 298 mph (480 km/h); service ceiling 29,660 ft (9040 m); initial climb rate 1,885 ft (575 m) per minute.

Range: Normal 1,084 miles (1745 km); Maximum (overload) 1,892 miles (3045 km) on internal fuel.

Weight: Empty 6,635 lbs (3010 kg) with a maximum take-off weight of 12,456 lbs (5650 kg).

Dimensions: Span 48 ft 10 1/2 in (14.90 m); length 35 ft 8 in (10.87 m); height 12 ft 5 1/2 in (3.80 m); wing area 400.42 sq ft (37.20 sq m).

Armament: One 7.7 mm (0.303 in) Type 98 machine gun manually aimed from rear cockpit and one manually aimed by middle crew member from rear ventral position and one fixed 7.7 mm (0.303 in) Type 98 machine gun in left wing (often absent from the B6N1). A 1,764 lbs (800 kg) 18 inch torpedo carried offset to the right of centreline, or six 220 lbs (100 kg) bombs carried under the fuselage.

Variants: B6N1 (Mamoru engined), B6N2 (Kasei engined), B6N2a, B6N3 (prototypes for land based version).

Avionics: Some later models were equipped with ASV radar for night operations.

History: First flight March 1941; service delivery (B6N1) early 1943; service delivery (B6N2) December 1943.

Operators: Japan (Imperial Japanese Navy).

Airwar Japan versus Allies

All English-language names for Japanese fighters derived from Western Allied identification codes, in which male names were given to enemy fighters and female names to Japanese bombers. The Japanese Naval Air Force (JNAF) Zero, or Mitsubishi A6M “Reisen” (Zero-Sen), was the best fighter available in the Pacific in 1941. It was lighter, faster, and more maneuverable than American land-based aircraft. It also had a much greater range and more nimble handling than any U.S. carrier-based fighters. That gave the Imperial Japanese Navy a critical advantage in early carrier vs. carrier fights such as Coral Sea . The Japanese Army Air Force ( JAAF) flew three models of the Nakajima Ki-43 “Hayabusa” (“Falcon”). Designated alternately as “Jim” or “Oscar” by the Western Allies, these land-based JAAF fighters saw most service in China and Southeast Asia, flying cover over ground forces. They faced handfuls of older Soviet and other fighters in China until the arrival of American pilots and modern aircraft of the American Volunteer Group, or “Flying Tigers” (“Fei Hu”). Japanese pilots in Hayabusa also faced RAF Spitfire and Hurricanes in Malaya and over Burma. Western pilots were initially shocked at the excellent performance of the Hayabusa, whose characteristics were not known to British or American military intelligence. The JAAF also flew the very fast “Hein,” which reached speeds above 400 mph. The “Frank” (Nakajima Ki84-Ia “Hayate”), introduced in 1944, and the excellent “George” (Kawanishi N1K1-J “Shiden”), introduced in 1944–1945, were also well-known to Allied sailors, troops, and flyers. But as improved as those aircraft were, neither model could match Western Allied fighters by that point in the war: the Japanese planes were relatively underarmored and undergunned, and by 1944 were usually flown by inexperienced, young pilots. However, over Japan the Hayate’s ceiling of nearly 38,000 feet and rocket weapons did pose a threat even to American B-29 bombers.

The USN F4F Wildcat was overmatched by Zeros in nearly all ways, an often fatal disadvantage not overcome by introduction of new American fighters for the first two years of the Pacific War. But the USN controlled the skies of the Pacific after powerful Pratt & Whitney engines were put into its heavily armored F6F “Hellcats” and F4U “Corsairs.” The combination of power, climb rate, ceiling, and arms and armament allowed those aircraft to master the fast but lightly armored Zero and to splash hundreds of slow IJN and Japanese Army bombers. The USAAF also had inadequate and mostly short-range fighters at the start of the war. But by war’s end, the USAAF boasted several of the fi nest and most effective fighters in the world. Many U.S. fighters were shipped to the Soviet Union under Lend- Lease, including 4,700 Bell P-39 “Airacobras” personally requested by Stalin. The P47 “Thunderbolt” and P51 “Mustang” dominated the skies of Italy, France, and Germany almost as soon as they were introduced in 1943. The P51 may have been the fi nest fighter of the war. It was equipped with long-range drop tanks that permitted it to escort strategic bomber formations deep into Germany and to the home islands of Japan. Both the P47 and P51 were also fitted with rockets and used in a “tank buster” role. In combination with late-war deterioration in Japanese aviator skills, better trained American pilots with new and better tactics in much improved machines achieved a 10:1 or higher kill ratio in Pacific War dogfights.

Air Operations Japan, Against (1942–1945)

On May 14, 1945 472 B-29s attacked the area in and around the Mitsubishi engine factory at Nagoya. Two nights later, another visit to Nagoya devastated another four square miles of that city. On May 23 and May 25, Tokyo was hit again. Although these two Tokyo raids had cost 43 B-29s, over 50 percent of the city had now been destroyed.

Alarmed at the increasing B-29 losses, a change of tactics was ordered. In an attempt to confuse the enemy defenses and to lure Japanese fighters into an air battle in which many of them would be destroyed, high-altitude daylight attacks were temporarily resumed. On May 29, 454 B-29s appeared over Yokohama, but this time they were escorted by P-51 Mustangs from Iwo Jima. In the resulting dogfight, 26 Japanese fighters were destroyed against the loss of four B-29s and three P-51s. Thereafter, the Japanese hoarded their surviving fighters for a last-ditch effort against the inevitable invasion force, and the air defense of cities became a lesser priority. By June of 1945, Japanese interceptors were seen much less frequently and the B-29s had free reign over all Japanese airspace.

#
Despite widespread awareness about the vulnerability of the Japanese home islands to air attack—reinforced by the results of the Doolittle Raid on Tokyo on 18 April 1942—U.S. plans for an air war against Japan remained vague until well into 1943 because of American limitations in resources and technology.

The development of the Boeing B-29 Superfortress changed this situation. Eventually, more than 1,000 of the long-range aircraft were deployed in the Twentieth Air Force under the direct control of the Army Air Forces commander, General Henry “Hap” Arnold, subdivided into the XX and XXI Bomber Commands. Under pressure to get results from his expensive very-heavy bomber program, he fielded the new aircraft even before testing had been completed.

In June 1944, B-29s from Major General Kenneth Wolfe’s XX Bomber Command began bombing Japan from China as part of Operation MATTERHORN. The campaign was plagued by logistical problems that got worse when Japanese troops overran advanced Allied airfields in China. Arnold replaced Wolfe with the USAAF’s premier problem-solver, Major General Curtis LeMay. However, even he could not make MATTERHORN a success. Arnold’s greatest hopes for an airpower victory over Japan rested with Brigadier General Haywood “Possum” Hansell’s XXI Bomber Command, which began operations from the Mariana Islands in November 1944. Hansell was one of the architects of the precision-bombing doctrine, but his operations also had little success.

Poor facilities, faulty training, engine failures, cloud cover, and jet streams at bombing altitudes made precision methods impossible. Hansell seemed unwilling to change his tactics, however, and Arnold feared that he would lose control of the heavy bombers to Allied Pacific theater commanders without better results, so he consolidated both bomber commands in the Marianas under LeMay and relieved Hansell.

LeMay instituted new training and maintenance procedures but still failed to achieve useful results with daylight high-altitude precision attacks. He decided to resort to low-level incendiary raids at night. Although area-firebombing went against dominant Air Forces doctrine, flying at low altitude reduced engine strain, required less fuel, improved bombing concentration, avoided high winds, and took advantage of weaknesses in Japanese defenses. LeMay’s systems analysts predicted that he could set large enough fires to leap firebreaks around important industrial objectives. His first application of the new tactics, Operation MEETINGHOUSE, against Tokyo on the night of 9 March 1945, produced spectacular destruction and was the deadliest air raid of the war.

Once enough incendiaries were stockpiled, the fire raids began in earnest. Warning leaflets were also dropped, which terrorized 8 million Japanese civilians into fleeing from cities. When General Carl Spaatz arrived in July to take command of U.S. Army Strategic Air Forces in the Pacific, including the Eighth Air Force redeploying from Europe, and to coordinate strategic air operations supporting the invasion of Japan, he had a directive to shift the air campaign from cities to transportation. But there was too much momentum behind the fire raids, sustained by operational tempo, training programs, and bomb stockage.

By the time Spaatz arrived, naval carrier strikes were also hitting key industrial objectives in Japan.More important, a submarine blockade had crippled the Japanese economy, the Russians were about to attack Manchuria, and Spaatz maintained direct command over the 509th Composite Group of B-29s specially modified to carry atomic bombs. Directed by Washington to deliver these weapons as soon as possible after 3 August, Spaatz ordered the attacks on Hiroshima and Nagasaki. These different elements combined with the incendiary campaign to comprise the series of blows that produced Japanese surrender.

As with the atomic bomb, there is still debate over the effects and morality of the firebombing raids. LeMay’s bombers burned out 180 square miles of 67 cities, killed at least 300,000 people, and wounded more than 400,000. His 313th Bomb Wing also sowed 12,000 mines in ports and waterways, sinking almost 1 million tons of shipping in about four months. LeMay remained convinced that his conventional bombing could have achieved victory by itself. LeMay, his tactics, and the legacy of the atomic bombs would be a primary influence in the shaping of the new United States Air Force.

References Hansell, Haywood S. Jr. Strategic Air War Against Japan. Washington, DC: U.S. Government Printing Office, 1980.

Colours of the Second Wave...

Dive-bombers – a comparison

The Aichi D3A (Val) dive-bomber entered service in 1940. In many ways similar to the German JU-87 Stuka, it was Japan’s top naval dive-bomber of the war and the most successful Axis warplane against Allied ships. An all-metal, low-winged monoplane with fixed landing gear, it was comparable to but somewhat lighter (at 8,047 pounds) than the Douglas SBD Dauntless of the United States (see below). The D3A (1,495 produced) was capable of 240 mph and a range of 915 miles. It was armed with three machine guns and carried one 551-pound bomb under the fuselage and two 132-pound bombs under the wings. A total of 126 Vals took part in the Pearl Harbor strike. Vals served throughout the war and were used at war’s end as kamikaze aircraft.

The United States lead the field, both in doctrine and equipment. The U.S. Marine Corps first used dive-bombers in action in Nicaragua in July 1927. By 1931, the U.S. Navy’s experiments with the Curtis Hawk caught the attention of the Japanese. They ordered two He50s from the German manufacturer Heinkel for their own tests. Within the next ten years both the U.S. and the Japanese navies had developed the Douglas SBD Dauntless (U.S. Army Air Forces designation: A-24) and the Aichi D3A Type 99 Val variants, respectively, that would serve each during much of the war. During the critical carrier battles of 1942 these two types of dive-bombers accounted for 70 percent of all ships sunk.

Most dive-bombers had similar specialized features. Steep dive angles were required both to ensure accuracy and to offer the minimal exposure to antiaircraft fire. In early models, however, the angle caused the bomb to damage or destroy the plane’s propeller as it left the aircraft. Bomb displacing gear (called a “fork” or “crutch”)—first added by the United States in 1931—threw the bomb clear of the propeller. Stability was paramount for accurate dive-bombing, but the slipstream from the wings buffeted the tail; therefore, dive brakes (perforated flaps along the wings’ trailing edge) were added.

The Dauntless was the standard U.S. Navy dive-bomber in 1941. It had a top speed of 250 mph and a loaded range of 1,300 miles. Dauntless variants included the scout (with 100- and 500-pound bomb combinations) and the bomber (one 1,000-pound bomb). The Val carried one 550-pound bomb at 240 mph to a range of 1,250 miles (five hours’ endurance), and it sank more Allied ships during World War II than any other Axis aircraft. It remained in production until the end of the war. Both the Dauntless and the Val had a crew of two and were difficult to shoot down when bombless, although neither had self-sealing fuel tanks. Midway through the war both navies fielded new but unsatisfactory dive-bombers, the Curtiss SB2C Helldiver and the Yokusaka D4Y Judy, respectively.

The Helldiver replaced the Dauntless, coming to the fleet in 1943. But its structural problems required major modifications, so it deployed in large numbers only in mid-1944. The Helldiver had an internal bomb bay and flew 20 mph faster than the Dauntless, but it carried the same bomb load; however, it was much harder to fly and maintain. Overall, it did not represent much of an improvement over the Dauntless. The Judy mounted the Japanese version of the engine which powered Messerschmidt fighters. Flying at 360 mph, it was by far the world’s fastest dive-bomber. Like the Helldiver, however, it had reliability problems. It was underarmored and also lacked self-sealing fuel tanks. The Judy never completely replaced the Val, anymore than the Helldiver replaced the venerable Dauntless.

Doctrinally, dive-bombers of both navies usually worked in close coordination with torpedo bombers and in many cases with level bombers and even high-altitude bombers. Because the defensive measures that ships took against each type of attacking aircraft were different, this combined-arms approach was very effective.

Early War Japanese Supremacy

 

At the beginning of the Pacific war neither Japan nor the United States possessed large numbers of warplanes, despite unprecedented programs of prewar aircraft development and production. Thus, early Pacific war air operations on both sides were undertaken with what were small forces compared with those engaged in Europe. Most British aircraft were, of course, in Europe, although there were air assets in Asia, in such places as Singapore, and Commonwealth air forces in Australia and New Zealand.

With long lead times in aircraft production from inception to production—up to four years for airframes and more than that for engines—timing and strategic decisions were extremely important. Both Germany and Japan caught aircraft modernization at the right time, that is, during the decade of the 1930s, when aircraft technology changed faster and more profoundly than at any time before or since. Furthermore, Japan’s penchant for secrecy enabled that country to keep the West unaware of what it had accomplished. Washington discounted reliable reports about the quality of Japanese aircraft, including reports from Claire Chennault, then supervising the Chinese air force.

Even though the Japanese air force was superbly equipped and trained at the outset of the conflict, it was in fact too small for world war. In December 1941 Japan had fewer than 3,000 combat-ready aircraft (the army had about 1,500 planes and the navy another 1,400). The vast majority of these were, however, of modern design (although several models with fixed, “spatted” landing gear gave a deceptively obsolete appearance) and were well suited for long-range operations. Japan emphasized maneuverability and long range in its fighters, and long range and bomb capacity in its bombers.

The weak design point of Japanese aircraft was their engines, in large part because of materials shortages, inferior lubricants, and inadequate quality control. Japan also continued to rely on prewar aircraft designs. Its basic design types—the Zero, the Betty, and the Val—all flew throughout the war. And Japan largely ignored defensive aircraft. Japan wanted a strike force capable of carrying out long-distance missions and inflicting maximum damage. Japanese pilots were superbly trained and had gained extensive combat experience against the Russians and the Chinese in the late 1930s, but Japan lost air supremacy in the great land-sea battles of 1942. Midway cost the navy four carriers and the lives of hundreds of experienced airmen. Guadalcanal was even more expensive; it became a “meat grinder” battle, in which Japan lost perhaps nine hundred aircraft, and, because Japanese bombers had relatively large crews (the Betty required seven men), it lost some twenty-four hundred trained pilots and aircrew. After Guadalcanal the United States launched many more carriers and vastly more aircraft (many of which were newer types), while the Japanese were forced for the most part to make do with updated versions of earlier aircraft, without veteran pilots to fly them.

By far the best and most famous Japanese fighter of the Pacific war was the Mitsubishi A6M Reisen (Zero, known as Zeke to the Americans but generally called Zero by all nations—eventually even by the Japanese, who nicknamed it Zero-sen). An excellent original design, it entered service in 1940. More Zeros (10,449) were built during the war than any other Japanese warplane. The A6M2 model that led the attack at Pearl Harbor had a speed of 332 mph and the exceptional range of 1,930 miles. It was exceptionally light; the fuselage was skinned with almost-paper-thin duralumin, and there was no seat armor; nor were its gas tanks self-sealing. At 6,264 pounds loaded, the A6M was almost half a ton lighter than the F4F Wildcat. It was also as maneuverable as any fighter of the war. The Zero had a surprisingly heavy armament—two 7.7-mm machine guns in the upper fuselage and two wing-mounted slow-firing 20-mm cannon. It could also carry 264 pounds of bombs. It was, however, deficient in structural strength. Based on bitter experience, U.S. pilots developed tactics to defeat the Zeros. Pairs of F4Fs, using the “Thach weave,” could handle four or five Zeros. The Zero went through a succession of models. The final (1945) A6M8 model had a 1,560-hp engine—60 percent more powerful than the engine in the A6M2—and could achieve 356 mph.

The main U.S. opponents of the Zero early in World War II were the army P-39 Airacobra and P-40 Warhawk and the navy/marine F4F Wildcat. The Bell P-39 Airacobra entered service in 1941. Its design centered on its unique armament—a 37-mm cannon firing through the middle of the nose cone—which dictated the entire structure of the aircraft. The engine was mounted in the center of the fuselage, behind the pilot, and the driveshaft to the propeller did double duty as a 37-mm cannon! The P-39 also had retractable tricycle landing gear positioned under its nose—the first such arrangement in a fighter. At 8,300 pounds, it was significantly heavier than the Zero, although its speed of 385 mph was faster. It had a range of 650 miles. The P-39 had one 37-mm cannon, four machine guns, and 500 pounds of bombs. No match for the Zero in one-on-one combat, the P-39 excelled in ground support operations. Of 9,558 P-39s produced during the war, fully half went to the Soviet Union for tactical support.

The Grumman F4F Wildcat entered service in December 1940. Powered with a 1,200-hp air-cooled engine, it was, at 7,000 pounds, only slightly heavier than the Zero and as fast as it (331 mph), but not nearly as maneuverable. Its range was 845 miles, and it was armed with six machine guns and 200 pounds of bombs. The F4F-4 (1941) had a speed of 318 mph and a range of 770 miles. The Wildcat was also quite strong. Although the Zero could easily outmaneuver the P-40 and F4F, U.S. Navy and Marine pilots developed tactics enabling them to utilize their heavy (.50-caliber) machine guns to cut the Zeros apart. The Wildcat was also faster than the Zero in a turning dive. The F4F remained in manufacture (8,000 produced) through the end of the war for service on escort carriers.