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G4M “Betty”, Japanese Medium Bomber


Photograph of G4M
                "Betty" bomber

militaryhistory.about.com

3-view diagram of G4M "Betty" bomber

U.S. Army. Via ibiblio.org


Mitsubishi G4M1 Model 11 "Betty"


Specifications:


Crew

7

Dimensions

82'0" by 65'8" by 19'9"
25m by 20m by 6m
Wing area 841 square feet
78 square meters

Weights

14,991-20,944 lbs
6800-9500 kg

Maximum speed      

266 mph at 13,780 feet
428 km/h at 4200 meters

Cruising speed

196 mph at 9,845 feet
315 km/h at 3000 meters

Climb rate

21 feet per second
6.4 meters per second

Service ceiling

30,000 feet
9100 meters

Power plant

Two 1530 hp (1141 kW) Mitsubishi MK4A Kasei 11 fourteen-cylinder air-cooled radial engines, driving three bladed metal propellers.

Armament

1 7.7mm Type 92 machine gun in the nose
1 7.7mm Type 92 machine gun in the dorsal blister
2 7.7mm Type 92 machine guns in the beam blisters
1 20mm Type 99 Model 1 cannon in the tail.

Bomb load

One 800 kg (1760 lb) torpedo or up to 800 kg (1760 lbs) of bombs.

Maximum range

3749 miles
6000 km

Fuel

962 gallons (3640 liters) in the wings.

Production

A total of 2,446 G4Ms and G6M1s were built by Mitsubishi Jukogyo K.K. as follows:

  2 12-Shi prototypes (Nagoya plant Sept 1939 and Feb 1940)
  30 G6M1 (Nagoya 1940)
  1,200 G4M1 (Nagoya Jan 1941-Jan 1944)
  1,154 G4M2 (640 at Nagoya and 514 at Okayama, Nov 1942-Aug 1945)
  60 G4M3 (Nagoya and Okayama Dec 1943-Aug 1945)

Variants

The G4M2 added two flexible nose 7.7mm machine guns and had a dorsal turret with a 20mm Type 99 Model 1 cannon. It used Kasei 21 engines driving four bladed metal propellers, and added doors to the bomb bay. Fuel capacity was increased to 1714 gallons (6490 liters) and the bomb load was increased to 1000 kg (2200 lbs).

The G4M2a used 1850 hp (1379 kW) Kasei 25 engines for improved fuel consumption and was fitted with improved bomb bay doors. It was armed with two nose 7.7mm machine guns and replaced the beam machine guns with 20mm cannon. Some were equipped with Type 6 surface search radar.

Starting with the G4M3, armor and self-sealing fuel tanks were added at the expense of fuel capacity (which dropped to 1186 gallons or 4490 liters).


The G4M "Betty" was just coming into service at the time of Pearl Harbor, and it became the backbone of the Japanese land-based naval bomber force. Like its predecessor, the G3M "Nell", it was built for range and speed and sacrificed almost all other qualities. However, it was much better armed than the Nell and had an internal bomb bay (albeit with no doors when loaded with ordnance.) Allied pilots quickly renamed it the One-Shot Lighter for its tendency to catch fire when hit; the Japanese nickname likewise translates roughly as Type 1 Zippo Lighter. The wing was designed as an integral fuel tank with a huge capacity, but it had only rudimentary self-sealing features, and this accounted for the incendiary qualities. Later versions sacrificed range for protection, but losses continued to be high.

The design originated in September 1937 when the Navy issued a specification to Mitsubishi for a replacement for the "Nell" with even greater range and speed. This required more than the 2000 hp available with existing engines, and the design team, led by Honjo Kiro, chose to use the new Kasei engine. The fuselage shape was designed for mass production. However, the prototype was not completed until September 1939 because the design team was splitting its efforts between the "Betty" and the A6M Zero. Production was further delayed by an unsuccessful experiment at designing a heavy escort fighter version of the G4M, the G6M, which ended up being used as a trainer and transport aircraft. The original G4M was finally put into production in 1940, with the first production aircraft coming out of factories in April 1941. Most of the early production went to French Indochina and Formosa and participated in the attack on Force Z and the destruction of American air power in the Philippines.

The failure of the G5N and G7M bomber projects meant that the G4M design continued to be refined throughout the war. Early versions had only rudimentary protection for the fuel tanks, consisting of rubber sheets on the bottom of the wing tanks and layers of rubber sheet and sponge around the fuselage tanks. The G4M3, which did not go into production until October 1944, included proper self-sealing fuel tanks and armor around the crew areas. Few were produced.

"Betty" was the plane Yamamoto and his staff were flying in when he was ambushed and killed off Buin in the Solomons.

"Betty" was the mother ship for the Ohka suicide aircraft, but the first Ohka raid lost 16 aircraft before they could get into launch position. This illustrates the continued fragility of "Betty" even with efforts to improve protection with armor and self-sealing fuel tanks.

Photo Gallery


G4M Betty side view

Wikimedia Commons

G4M Betty side view

Wikimedia Commons

G4M Betty ventral view

Wikimedia Commons

Tail gunner position

Wikimedia Commons

G4M Betty side view

Wikimedia Commons

G4M Betty page from FM 30-30

U.S. Air Force

FM 30-30 page on G4M Betty

U.S. Air Forc

References

Bergerud (2000)

Francillon (1979)
Peattie (2001)



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