Copyright 2008 by Brandon Cope

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Mitsubishi G4M "Betty" medium bomber

The G4M was the principle Imperial Japanese Navy medium bomber of the war, operated from land bases. It originated in a 1937 request for a bomber with a longer range and higher speed than the G3M. To meet this requirements, weight had to be shaved and this meant no armor protection for the fuel tanks or crew. The unprotected large wing tanks in particular proved to be vulnerable, resulting in many encounters with Allied fighters turning the Betty into a flaming coffin. Also, after 1942, as the Japanese were forced on the defensive, the long range of the G4M became less and less of an advantage.

However, early in the war the G4M gave valuable service. It participated in the sinking of the HMS Prince of Wales and Repulse in December 1941, as well as the first air raid on Darwin, Australia. Some 1,150 of the G4M2 were built.

An additional 420 gallons of fuel could be carried in place of the bomb load. A 1,764-lb torpedo could be carried externally instead of a bomb load.

The G4M2 has a crew of seven: Pilot, co-pilot, navigator (who also acts as bombardier and operates the two forward Type 92's), radio operator (who also mans the dorsal turret) and three gunners (two wasit positions and the tail). The G4M2 uses 134 gallons of aviation fuel per hour at routine usage.

Subassemblies: Heavy Fighter-Bomber chassis +4, Light Bomber Wings +4, 2xSmall AFV Engine Pods +2, full rotation Medium Weapon turret +1, three retractable wheels +1.
Powertrain: 2x1,341-kW aerial HP supercharged gasoline engines [Pods] with 2x1,341-kW props, and 1,294-gallon standard fuel tanks [Body and Wings], 4,000-kw batteries
Occupancy: 7 CS  Cargo: 19 Body.

Armor
All: 2/3

Weaponry
2xAircraft LMG/Type 92 [Body:F] (1,164 each)
Aircraft LMG/Type 92 [Body:L] (1,164)
Aircraft LMG/Type 92 [Body:R] (1,164)
20mm Short Aircraft AC/Type 99-1 [Turret::F] (125)
20mm Short Aircraft AC/Type 99-1 [Body:B] (125).

Equipment
Body: Large radio receiver and transmitter, navigation instruments, autopilot., bombsight, 2,200-lb bomb bay.

Statistics

HT: 8.
HP: 525 [body], 300 [each wing], 150 [each pod], 50 [each wheel]
 

Design Notes
Design speed was 299 mph. The historical speed has been used, as well as the actual wing area (841 square feet). To better match historical weight, wing cost, weight and HPs were divided by 2. In the end, loaded weight was increased by only 2%

Typical internal bombload was ten 100 kg bombs.

Variants

The G4M1 Model 11 (1941) lacked a dorsal turret, having a blister instead. The dorsal position was armed with only single 7.7mm Type 92 MG. They reached 266 mph powered by unsupercharged 1,140-kW engines. Bombload was only 1,800 lbs. Some 400 were built. The Model 12 (1942) added superchargers, for better high altitude performance. Some 770 were built. In 1943, DR 10 armor was added to the underside of the wing tanks and the rear gunner position, which reduced top speed by 6 mph.

The G4M2 Model 22A Ko replaced the waist 7.7mm Type 92's with 20mm Type 99-1's.

The G4M2 Model 22B Otsu had more powerful Type 99-2 (20mm Medium Aircraft ACs) in all four cannon positions.

The G4M2a Model 24 used slightly more fuel efficient engines rated at 1,361-kW. The Model 24A and Model 24B were armed similar to the 22A and 22B. The 22C replaced the two nose LMGs with a single 13.2mm Type 2 HMG (Medium Aircraft HMG).

The G4M2e Model 24J were conversions of many 22B and 22C to carry the Okha suicide bomb. The fuselage fuel tank was self-sealing and the pilot/copilot had DR 20 armor.

The G4M3 Model 34 (1944) belatedly added self-sealing tanks and armor protection (DR 20) for the crew. It also replaced the waist 7.7mm Type 92's with 20mm Type 99-1's. The plane reached 292mph with 1,361-kW engines. Only 60 were built.