Modern-Aviation

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.

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 series was begun late in 1937 at the request of the Japanese Navy, which wanted a land-based bomber that was even better than the excellent G3M then entering service. High speed and long range were the chief requirements. The new aircraft was to reach a speed of 250 mph (400 km/h) at 10,000 ft (3,000 m), have a range of 3,000 miles (4,800 km) without payload and 2,300 miles (3,700 km) with a 1,760-pound (800 kg) torpedo. Designer Kiro Honjo solved the problems involved with great skill. The first of two prototypes took to the air for the first time on October 23, 1939.

Only a few minor changes were required, and during flight tests the aircraft easily met the specifications. The second prototype touched 278 mph (445 km/h) and demonstrated a range of more than 3,400 miles (5,500 km).

Before the bomber went into production, attempts were made to develop a heavy escort fighter version of the G4M1. Mass production of the bomber began in 1940, and the first exampIes came off the production line in April 1941. The Mitsubishi Betty made its operational debut in the last phases of the war against China, and when Japan and America went to war the G4M1 had a great weight of operational experience behind it. This expertise and the type’s long range were responsible for its great success, particularly during the first year of the war in the Pacific. G4Ms played a major role in the sinking of the British battleships Prince of Wales and Repulse on December 10, 1941.

Combat experience and the discovery of weak points such as a lack of armour led to the development of a more powerful and improved version in 1942. This was the G4M2, of which a total of 1,154 were built. The final version, the G4M3, appeared late in 1944. Only 60 of this variant were built.

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.

Nicknamed the ‘Flying Cigar’ on account of its shape and because the fuel tanks were unprotected and easily caught fire, the Mitsubishi G4M was nevertheless the most famous and most numerous Japanese bomber of the war. A total of 2,446 were built in several versions between September 1939 and August 1945. The aircraft saw service from the first day of the war to the last, when two white-painted G4M1s, bearing green surrender crosses instead of the Rising Sun, carried the Japanese delegation to its final appointment with the Allies. The ‘Betty’, as the Mitsubishi bomber was called in the Allied code, proved itself an excellent combat aircraft on all fronts. Its outstanding range literally revolutionised operational concepts in the Pacific.

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.