The Nakajima B5N 

Allied codename 'Kate'

Japan
Japan

Sorry, No ID pictures yet

The Imperial Japanese navy air force issued a requirement for a new carrierborne torpedo bomber in 1932. Three companies reacted: Aichi, Mitsubishi and Nakajima. Each of these built a single prototype, but none of these were deemed satisfactory, however, and the navy thus issued a 1934 requirement for a more capable type to replace the obsolescent Yokosuka B3Y.
The design selected for production was the Yokosuka B4Y, but this was regarded only as an interim type as the Imperial Japanese Navy wanted a torpedo bomber offering greater compatibility of performance with the Mitsubishi A5M monoplane fighter.
In 1935, therefore, the Imperial Japanese Navy Air Force issued its requirement for a three-seat attack warplane with folding wings and the ability to carry a 1,764 lb (800 kg) torpedo or an equivalent weight of bombs at a maximum level speed of 207 mph (333 km/h) at 6,560 ft (2.000 m) with a powerplant of one Nakajima Hikari or Mitsubishi Kinsei radial engine. This new requirement resulted in designs from Mitsubishi and Nakajima, the latter’s offering being the Type K design created by a team under the supervision of Katsuji Nakamura.
The Type K was a cantilever low-wing monoplane of basically all-metal construction with fabric-covered control surfaces, and included among its more advanced features wide-track main landing gear units that hydraulically retracted inward, and outer wing panels that folded upward and inward with the starboard wing under the port wing. The core of the structure was the oval-section fuselage, which was of semi-monocoque construction with accommodation for the crew of three in a long cockpit under a ‘glasshouse’ canopy with sliding sections to provide means of entry and exit. This core section carried the flying surfaces, which comprised a perfectly conventional tail unit with a mid-set tailplane, and the wing. This was based on a flat center section with tapered leading and trailing edges, and dihedraled outer panels that were tapered in thickness and chord. The center section carried trailing-edge Fowler flaps while the outer panels, outboard of the wing fold hinge lines, carried trailing-edge ailerons.
The B5N1 prototype made its first flight in January 1937 with a powerplant of one Nakajima Hikari 2 radial engine, driving a three-blade metal propeller of the variable-pitch type.

Version list:

Further pictures:

A flight of Nakajima B52N's on their way. I wonder what their target was…
A flight of Nakajima B52N's on their way. I wonder what their target was…

A Nakajima B5N1 on an airfield
A Nakajima B5N1 on an airfield

 

Technical data on the Nakajima B5N1
Powerplant 1 × Nakajima Hikari 3 nine-cylinder air-cooled radial, rated at 840 hp (626.21 kW) Role during war
  • Torpedo Bomber
  • U-boat Destroyer
  • Maritime/Coastal patrol reconnaissance Bomber
Length 33 ft 9.5 inch Height 12 ft 1.75 inch
Empty weight 4643 lb Operational weight 8157 lb typical,
8852 lb max
Wing Span 50 ft 10.9 inch unfolded, less than 24 ft 7.9 inch folded. Wing Aspect ratio 6.39
Wing Area 405.798 sq ft Service ceiling 24280 ft
Maximum speed 229 mph at 6560 ft Cruising speed 159 mph at 6560 ft
Initial climb rate Climb to 9,845 ft in 7 min 50 sec Range 679 miles typical,
1404 miles max
Fuel capacity internal 255 Imp gal (306 US gal) Fuel capacity external -
Machine guns
  • 1 × 0.303 inch Type 92 trainable rearward-firing in the rear cockpit
Cannons -
Bomb load Up to 1,764 lb, carried on one under fuselage hardpoint rated at 1,764 lb. General disposables load consisted of:
  • 2 × 551 lb bombs typically
Torpedoes/rockets
  • 1 × 1,764 lb torpedo in stead of bombs
Crew 3: pilot, navigator/bombardier/observer, radio operator/gunner Naval or ground based Ground and Naval
First flight (prototype) Januari 1937 Operational Service 1938 - 1945
Manufacturer Nakajima Hikoki K.K. Number produced 1,149 total, unknown out of 669 B5N1, B5N1-K and B5N2 this version
Metric system
Length 10.3 m Height 3.7 m
Empty weight 2106 kg Operational weight 3700 kg typical,
4015 kg max
Wing Span 15.52 m unfolded, less than 7,5 m folded. Wing Aspect ratio 6.39
Wing Area 37.7 m² Service ceiling 7401 m
Maximum speed 369 km/h at 1999 m Cruising speed 256 km/h at 1999 m
Initial climb rate Climb to 3.000 m in 7 min 50 sec Range 1093 km typical,
2259 km max
Fuel capacity internal 1.160 liters Fuel capacity external -
Machine guns
  • 1 × 7,7 mm Type 92 trainable rearward-firing in the rear cockpit
Cannons -
Bomb load Up to 800 kg, carried on one under fuselage hardpoint rated at 800 kg. General disposables load consisted of:
  • 2 × 250 kg bombs typically
Torpedoes/rockets
  • 1 × 800 kg torpedo in stead of bombs

Technical data on the Nakajima B5N2
Powerplant 1 × Nakajima NK1B Sakae 11 fourteen-cylinder air-cooled radial, rated at 1000 hp (745.49 kW) Role during war
  • Torpedo Bomber
  • U-boat Destroyer
  • Maritime/Coastal patrol reconnaissance Bomber
Length 33 ft 9.5 inch Height 12 ft 1.75 inch
Empty weight 5024 lb Operational weight 8378 lb typical,
9039 lb max
Wing Span 50 ft 10.9 inch unfolded, less than 24 ft 7.9 inch folded. Wing Aspect ratio 6.39
Wing Area 405.798 sq ft Service ceiling 27100 ft
Maximum speed 235 mph at 11810 ft Cruising speed 161 mph at 9845 ft
Initial climb rate Climb to 9,845 ft in 7 min 40 sec Range 608 miles typical,
1237 miles max
Fuel capacity internal 255 Imp gal (306 US gal) Fuel capacity external -
Machine guns
  • 1 × 0.303 inch Type 92 trainable rearward-firing in the rear cockpit
Cannons -
Bomb load Up to 1,764 lb, carried on one under fuselage hardpoint rated at 1,764 lb. General disposables load consisted of:
  • 2 × 551 lb bombs typically
Torpedoes/rockets
  • 1 × 1,764 lb torpedo in stead of bombs
Crew 3: pilot, navigator/bombardier/observer, radio operator/gunner Naval or ground based Ground and Naval
First flight (prototype) Januari 1937 Operational Service 1938 - 1945
Manufacturer Nakajima Hikoki K.K. Number produced 1,149 total, 480 + unknown out of 669 B5N1, B5N1-K and B5N2 this version
Metric system
Length 10.3 m Height 3.7 m
Empty weight 2279 kg Operational weight 3800 kg typical,
4100 kg max
Wing Span 15.52 m unfolded, less than 7,5 m folded. Wing Aspect ratio 6.39
Wing Area 37.7 m² Service ceiling 8260 m
Maximum speed 378 km/h at 3600 m Cruising speed 259 km/h at 3001 m
Initial climb rate Climb to 3.000 m in 7 min 40 sec Range 978 km typical,
1991 km max
Fuel capacity internal 1.160 liters Fuel capacity external -
Machine guns
  • 1 × 7,7 mm Type 92 trainable rearward-firing in the rear cockpit
Cannons -
Bomb load Up to 800 kg, carried on one under fuselage hardpoint rated at 800 kg. General disposables load consisted of:
  • 2 × 250 kg bombs typically
Torpedoes/rockets
  • 1 × 800 kg torpedo in stead of bombs

Here is a quick overview of all different versions, without the full technical specifications:

Different versions of the Nakajima B5N 
Nakajima B5N1 This version was the result of a somewhat staggered design cyclus. The first designs by several companies were all rejected, the second round of designs only resulted in an interim type. Finally, five years after the initial requirement a suitable type was found in the form of the B5N Kate. The B5N1 was the first production version, for technical details see above.
Number built: unknown out of 669
Nakajima B5N1-K This version was specifically built for training purposes. No further details are known.
Number built: unknown amount out of 669
Nakajima B5N2 The B5N1 showed that moderately modern fighters were too dangerous to the B5N1, and in 1939 a variant was designed. The resulting B5N2's engine was more powerful and smaller in diameter (double row of 7-cylinders, as opposed to 9 cylinders), which enabled the engineers to design a smaller cowling. this improved the pilot view and reduced drag. A small spinner was added to the propeller, which reduced drag even further and improved the cooling of the engine
Although the new engine had more than 36% increase in power, the B5N2 was only marginally faster than the B5N1. yet the new version was placed into production, because the Sakae engine was more reliable than the Hikari. This of course was a very important asset for a single-engined aircraft that was to fly long stretches over water.
Number built: 480 plus an unknown amount out of 669
Navy Type 97 Carrier Attack Bomber Model 1 Official Imperial Japanese Navy Air Force designation for the Nakajima B5N1
Navy Type 97 Carrier Attack Bomber Model 11 Revised official Imperial Japanese Navy Air Force designation for the Nakajima B5N1.
Navy Type 97 Carrier Attack Bomber Model 12 Official Imperial Japanese Navy Air Force designation for the Nakajima B5N2.
Navy Type 97-1 Carrier Attack Bomber Official Imperial Japanese Navy Air Force designation for the Nakajima B5N1. The Type 97-2 Carrier Attack Bomber was the official designation for the Mitsubishi B5M1
Navy Type 97-3 Carrier Attack Bomber Official Imperial Japanese Navy Air Force designation for the Nakajima B5N2.

Operational remarks:

Like almost all Japanese aircraft, the B5N were most succesfull during the early War years. The B5N1 entered service as a land-based as well as carrierborne bomber, in the former capacity serving as a level bomber in the early stages of the Second Sino-Japanese War (1937 - 1945). Here the B5N1 proved moderately successful, especially when escorted by A5M fighters, but by 1939 it had become clear that the lack of crew and fuel tank protection was a tactical liability that could only be offset by the provision of such protection. This would mean an increase in weight and subsequently a reduction in performance and agility. The Japanese decided not to do so, placing a greater importance on speed and maneuverability.
By the time the Japanese attacked Pearl Harbor, all B5N1's had been withdrawn from first-line service, and had been replaced by B5N2's. On 7 December 1941 144 B5N2's were among the Japanese attackers on Pearl Harbor, and these made short work of the US fleet anchored there. In the year to come the B5N2's claimed more victories, amonsgt others three US Navy aircraft carriers, the Lexington, the Yorktown, and the Hornet during three separate encounters.
The type also operated in the land-based role, suffering very heavy losses in the campaign that followed on the US invasion of the Philippine islands in October 1944. The B5N was then withdrawn from bomber service only to be pressed into service as an anti-submarine type. This role had been suggested by the B5N2’s long endurance (minimal 4 hours, maximal 7 hours, depending on height and speed) and adequate payload capability. The aircraft were modified with either air-to-surface search radar, using antennae on the sides of the rear fuselage and along the wing leading edges, or with the Jikitanchiki magnetic anomaly detection system. Other aircraft were adapted as trainers, target tugs and glider tugs along the line of the B5N1-K.

Strengths:

Weaknesses:

 

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© by Frans Bonné, 2000
Last revision: 9/23/01