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Mitsubishi G4M (Betty)

Navy Land-Based Medium Bomber Aircraft

The Mitsubishi G4M Betty will forever be linked to the ill-fated flight which saw the death of Japanese Admiral Yamamoto at the hands of American Lockheed P-38 Lightning fighters over Bougainville in 1943.
Authored By: Staff Writer | Edited: 5/21/2018
National Flag Graphic


Year: 1941
Status: Retired, Out-of-Service
Manufacturer(s): Mitsubishi - Japan
Production: 2,435
Capabilities: Ground Attack; Navy/Maritime;
Crew: 7
Length: 65.45 ft (19.95 m)
Width: 82.02 ft (25 m)
Height: 16.08 ft (4.9 m)
Weight (Empty): 14,859 lb (6,740 kg)
Weight (MTOW): 28,329 lb (12,850 kg)
Power: 2 x Mitsubishi MK4P Kasei 21 air-cooled radial piston engine developing 1,800 horsepower each.
Speed: 267 mph (430 kph; 232 kts)
Ceiling: 27,887 feet (8,500 m; 5.28 miles)
Range: 1,771 miles (2,850 km; 1,539 nm)
Rate-of-Climb: 1,800 ft/min (549 m/min)
Operators: China (post-war); Imperial Japan; Indonesia (post-war); United Kingdom (tested); United States (tested)
Like most of Imperial Japan's aircraft in the early stages of World War 2, the Mitsubishi G4M (codenamed "Betty" by the Allies) was a potent performer in operation as a twin-engined, land-based naval medium-class bomber. The aircraft was of a well-thought out design, showcasing excellent range for the period and would see combat action throughout the entire war. Though appearing in relatively limited numbers (just over 2,400 were built), the G4M - at least for a time - was a medium bomber of considerable value to the Empire of Japan when attempting to retain its holdings across the vast Pacific.

Despite this early wartime success, the series is mainly remembered as one of two "Betty" aircraft shot down by a pair of American P-38 "Lightning" fighters on April 18th, 1943. One of the bombers was of particular note for its passenger was none other than Japanese Admiral Isoroku Yamamoto - mastermind of the Pearl Harbor attack of December 1941 - a disastrous blow to Imperial Japanese operations in the Pacific Theater. The P-38 pilots credited with the attack were 1st Lt. Rex T. Barber and Captain Thomas G. Lamphier intercepting from Henderson Field, Guadalcanal.

Mitsubishi engineers developed their G4M to fulfill a 1937 requirement calling for an all-modern long-range bombing platform. The prototype recorded a first-flight on October 23rd, 1939 and did not disappoint - proving the design capable of possessing both above average speed as well as range. Defensive armament consisted of a combination of cannon and machine guns: 1 x 7.7mm Type 92 machine gun was positioned at the nose and one at the dorsal turret. One gun was managed at each beam position (side blisters). 1 x 20mm Type 99 automatic cannon was featured at a gunner's position in the tail to protect the aircraft's critical "six". The crew commitment was seven (2 x pilots, nose gunner-bombardiers-navigator, dorsal gunner, 2 x waist gunners, tail gunner) and an internal bomb load of up to 2,205 pounds could be carried. With the bomber being developed for the Imperial Japanese Navy, and therefore charged with attacking naval targets of interest, the G4M was also cleared to carry a 1,858lb Type 91 torpedo in place of the traditional conventional drop bomb load.

The G4M prove its worth immediately in early entanglements that included the sinking of the British warships HMS Repulse and HMS Prince of Wales, both occurring in the first year of the aircraft's combat service career. In addition to successful action against the Allies, the G4M was also used in anger against neighboring China in their long-running war.

The primary weakness of the G4M, a weakness common to many of the Japanese aircraft of the Second World War, was armor protection of crew spaces and fuel stores. Lacking these qualities, the aircraft proved highly susceptible to small bursts of gunfire. Any sort of dominance that the G4M exhibited in the early phases of the conflict were soon reversed as newer and better Allied fighters became available in quantity. The days of the G4M as a frontline attack system were numbered though the series saw action into the war's final weeks (August 1945

Variants included the G4M1 (encompassing prototypes and the first production model), the G4M2 (various sub-marks produced for Navy service), the G4M3 (self-sealing fuel tanks and armor protection added) and the G6M1 (improved defensive armament, 30 built).

With its pair of Mitsubishi MK4A-11 "Kasei" 14-cylinder radial engines of 1,530 horsepower each, the G4M1 (Model 11) managed a maximum speed of 265 miles per hour (cruising at 195mph), a range out to 1,770 miles and a service ceiling up to 28,000 feet. Rate-of-climb was 1,800 feet-per-minute.

The Betty stocked some 37 Japanese bomber groups during the war. Post-war operators became China and Indonesia. Both the United States and United Kingdom tested the aircraft extensively.

Production totaled 2,435 units. This included 1,172 of the definitive G4M1 mark, 429 examples of the G4M2, 713 additional aircraft in the G4M2a guise and 91 examples of the G4M3. The G6M1 numbered thirty aircraft.


1 x 7.7mm Type 92 machine guns in nose.
1 x 7.7mm Type 92 machine gun in dorsal turret.
1 x 7.7mm Type 92 machine gun at left-beam position.
1 x 7.7mm Type 92 machine gun at right-beam position.
1 x 20mm Type 99 automatic cannon in tail gun position.

Maximum internal bomb loadout of up to 2,205lbs OR 1 x 1,858lb Type 91 aerial torpedo in place of bombs for anti-shipping sorties.

Graphical image of an aircraft medium machine gun
Graphical image of an aircrat automatic cannon
Graphical image of an aircraft anti-ship missile
Graphical image of an aircraft aerial torpedo
Graphical image of an aircraft conventional drop bomb munition

Variants / Models

• G4M1 - Prototype Model Designation; first flight October 23, 1939; produced in variant Model 11 and Model 22 detailed below; 1,200 examples produced.
• Navy Type 1 Attack Bomber Model 11 - Initial Production Models.
• Navy Type 1 Attack Bomber Model 22 - Second Production Models featuring revised engines.
• G4M2 - "Improved" G4M1 Models; produced in variant Model 22A and Model 22B detailed below; 1,154 examples produced.
• Navy Type 1 Attack Bomber Model 22A - Featured Mitsubishi Kasei radial engines of 1,800 horsepower; defensive armament revised along with increased fuel capacity.
• Navy Type 2 Attack Bomber Model 22B - Similar to Model 22A.
• Navy Type 1 Attack Bomber Model 24 - "Improved" G4M2.
• G4M3 - "Improved" G4M2 Models
• Navy Type 1 Attack Bomber Model 34 (G4M3); 60 examples produced.
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