Mitsubishi G4M

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 land-based naval bomber. The system was of a strong design and featured impressive range for the time and would see combat action throughout the entire war. Though appearing in limited numbers, the G4M - at least for a time - was a weapon to be reckoned with. The G4M was designed for a long range and high speed at the time of its introduction. Consequently, several weight-saving measures were incorporated into the design, such as dispensing with self-sealing fuel tanks and armor, which caused Allied fighter pilots to give it derisive nicknames such as 'the one-shot lighter', 'the flying Zippo' and 'the flying cigar' because of their tendency to explode or catch on fire from any slight damage to the wing fuel tanks after being hit by aerial machine gun fire or ground-based anti-aircraft fire. Similarly, pilots of the Imperial Japanese Navy despairingly called the G4M the 'Type One Lighter', 'The Flying Lighter' or even the 'Hamaki' ('Cigar'). This was partially due to the fact that on many occasions, the G4M was used for low-altitude torpedo attacks on ships during which their performance advantages were negated.

The G4M started as a product of the Mitsubishi company, charged with filling the 1937 requirement calling for a capable long-range bomber aircraft. The system first flew in mid-October of 1939 and did not disappoint - proving the design capable of possessing both above average speed and range. Defensive armament consisted of a combination of cannon and machine guns. 2 x 7.7mm machine guns were positioned in the nose and two side blisters (one gun per blister). A single cannon was placed in the dorsal turret and in the tail gun position. Crew accommodations amounted to seven personnel and an internal bomb load of up to 2,205 pounds was afforded. With this design being of naval origins, the Betty was also slated to carry up to 1 x 1,764 anti-ship torpedo in place of the traditional bomb load. The G4M was similar in performance and missions to other contemporary twin-engine bombers such as the German Heinkel He 111 and the American North American B-25 Mitchell. These were all commonly used in anti-ship roles. The G4M Model 11 was prominent in attacks on Allied shipping in the 1941 to early 1944, but after that it became more and more an easy prey for Allied fighters. Protection in the way of additional armor given to the crew and the fuel tanks were usually sub-standard when compared to its contemporaries. As such, the system proved to be highly susceptible to Allied gunfire with relative ease. Any sort of dominance that the G4M exhibited in the opening years of the conflict were soon reversed as the newer and better Allied fighters were made available in any kind of concentrated number across the Pacific. Engine-power and fuel capacity were increased with the G4M2, this version was produced in the greatest numbers. In the G4M3 the balance of the design was dramatically changed, with full protection being provided and fuel capacity being drastically reduced.

The Japanese Navy had found itself a capable performer and the G4M began to prove its worth in early entanglements that included the sinking of the British warships HMS Repulse and the HMS Prince of Wales off the eastern coast of British Malaya on 10 December 1941. The G4M's baptism of fire occurred on 13 September 1940 in Mainland China, when 27 "Betties" and Mitsubishi C5Ms of 1st Rengo Kokutai (a mixed force including elements of the Kanoya and Kizarazu Kokutais (Air Groups)) departed from Taipei, Omura, and Jeju City to attack Hankow. A similar operation occurred in May 1941. In December 1941, 107 G4Ms based on Formosa of 1st Kokutai and Kanoya Kokutai belonging to the 21st Koku Sentai (Air Flotilla) crossed the Luzon Strait en route to bombing the Philippines, and this was the beginning of the large-scale invasion of the islands of the Southwest Pacific Theater. On 8 August 1942 during the second day of the U.S. Marines landing on Guadalcanal, IJNAS's 23 G4M1s conducted a torpedo attack against American ships at Lunga point, Guadalcanal. A total of 18 of the attacking G4M1s were shot down, due to very heavy anti-aircraft fire, and air attacks from Grumman F4F 'Wildcat' fighters based on three American aircraft carriers. In all 18 Japanese crews approximately 120 aviators were missing at the beginning of August 1942. More than 100 Japanese G4M1s and their best pilots and crews (with no replacements or substitutes available) were shot down during the subsequent numerous battles on and near Guadalcanal (August to October 1942). In the two days of the Battle of Rennell Island, 29 and 30 January 1943, 10 out of 43 Japanese G4M1s were shot down during night torpedo attacks, all by U.S. Navy anti-aircraft fire.
Probably the best-known incident involving a G4M during the war was the attack resulting in the death of Isoroku Yamamoto. The G4M with tail number T1-323 - which was carrying the Imperial Japanese Navy Admiral Isoroku Yamamoto - was attacked and shot down by Lockheed P-38 'Lightnings' from the 339th Fighter Squadron of the 347th Fighter Group, Thirteenth Air Force, USAAF on 18 April 1943.
Back to Top
Following the loss of Okinawa, G4Ms constituted the main weapon of the land-based Japanese naval bomber force, which consisted of 20 Kokutais at the end of the war, including the testing air group equipped in 1944-'45 with the latest version G4M3 Model 34 and 36 which arrived too late to have an impact on the war. From November 1944 to January 1945, G4Ms were one of the main types of aircraft used in the Japanese air attacks on the Marianas Islands. Other G4Ms received field modifications resulting in the Model 24J which carried the Yokosuka MXY7 Ohka Model 11 suicide flying bombs beginning on 21 March 1945, with disastrous results due to extensive Allied fighter opposition.

The G4M had very good performance, especially range, which was achieved by its structural lightness and an almost total lack of protection for its crew, with no armor plating or self-sealing fuel tanks. These omissions proved to be its weakness when confronted with American fighter aircraft during the Pacific War. The G4M was frequently shot down by anti-aircraft artillery fire, and even by small arms. The G4M's relatively large size made it an easy gunnery target, and the predictable approach path required for a torpedo run made for a generally easy interception by Allied fighter aircraft. Nearly 2500 G4Ms were built during the war, about half as the earlier G4M1 version, and the rest mainly G4M2s and less than 100 G4M3s.