Mitsubishi G4M (1939)

Twin engine Naval Bomber 1939-1945: 2,435 Made.

The Mitsubishi G4M (allied conename "Betty") was the replacement for the 1930s G3M ("Nell"), as the primary land based bomber of the Imperial Japanese Navy. The Mitsubishi Navy Type 1 attack bomber nicknamed "Hamaki" as it was far more "fattier" than the nimble G3M, was also far more powerful and it boasted good performance across the board. It was considered the world's best land-based naval bomber, in a category that pretty much only existed in Japan. However like may Mitsubishi production that traded for a lightweight strcuture for speed, it was criticized for its flimsy construction, lack of crew or fuel tanks protection. Introduced on 2 April 1941, it was soon derided by allied pilots as the "The Flying Lighter", prone to ignition after a few hits. Only with the G4M2 and G4M3 these issues were solved. With 2,435 delivered until 1945, it was also the most common of its type.

The Prime IJN Land-Based Bomber

The Mitsubishi G4M was designed in 1937-38 already as a replacement for the earlier G3M, already an important asset for Yamamoto in its Pacfc grand strategy, giving the fleet a reach equivalent to aircraft carriers, but from captured airbases dotted across islands. At the time, the IJNAS, the air service branch of the Imperial Japanese Navy was the only one across the globe to feature large numbers of land-based bombers. That category was indeed as much as forbidden by law in the US (reserved for the USAAC) and in Britain, the Fleet Air Arm was only authorized seaplane bombers instead. But the rivalry between the Army and Navy resulted in this unique case of entirely separated air service branches. The G3M developed in 1933-34 was already largely inspired by Junkers airplanes, which patents were acquired from 1928, and this culminated with the very aerodynamic Mitsubishi Ka-9. The core idea was to design a bomber so fast it did not needed an escort.

Production of the G3M started via the Ka-15 and pre-series, really starting in 1936, then going on with improvements until 1943, with transport versions developed on that base. However by 1942 standards it was already considered too slow and undepowered. Its replacement was planned long in advance by Yamamoto, which wanted a faster and more powerful model, which would be still a twin-engine, land-based medium bomber. The Mitsubishi Aircraft Company was not firmly chosen at first, but a string contender to deliver this successor for the Air Service (IJNAS) with a scheduled debut date FY1940. The base design of the G3M was improved across the board, and it was fitted with engines almost twice as powerful. The end product, that first flew in 1939, became the Mitsubishi Navy Type 1 attack bomber (Ichishiki rikujō kōgeki ki, Isshikirikukō). But in service the G4M1 was soon hated or derided by lany IJN pilots when compared to the more graceful G3M. It was nicknamed "Hamaki" ("cigar") between its barrel-like fuselage shape and tendency to ignite if hit. As soon as it was spotted, the Allied reported its name as "Betty". It soon became a familiar codename in operaton as the G4M was virtually everywhere during the war.

The G4M was indeed designed to succeed the Mitsubishi G3M and concentrate better performances overall, excellent range and better payload. It was soon considered the best land-based naval bomber, boasting an agility that would leave 1941 allied fighters like the Buffalo and Wildcat, in the dust. The reality was severe however. Compromises made in its flimsy structure (like for the Zero) led to an almost total lack of crew protection, no armor plating, not even self-sealing fuel tanks, which became the norm in 1937-38 already. The G4M took its sweet time in development until finally declared ready for service and accepted by the IJNAS on 2 April 1941. If lightweight made sense for a dogfighter like the Zero, this was a death sentence of a bomber, as fighters would always catch up. The result was heavy losses, so much so, Allied fighter nicknamed the Betty "The Flying Lighter". It took a more year for Mitsubushi to start better protecting it, with the G4M2 and G4M3 (self-sealing fuel tanks, armor protection, better defensive armament), compensating for the extra weight with better engines.

Despite its youth issues, the G4M soon became the IJNAS' primary land-based bomber, bringing an unrivalled bombing capacity at long distances and another asset in the IJN arsenal, complementary alongside the Kido Butai (IJN carrier group). This becale most widely produced and most famous Japanese bomber in world War II, reflecting the same path a the A6M in its field. The G4M took part in virtually all battles of the Pacific War, taking part for example to the sinking of Force Z (HMS Prince of Wales and Repulse) a world's first in the open sea. G4Ms would operate alongside G3Ms there and later to sink USS Chicago at the Battle of Rennell Island. As the G4M replacement was already on its way, between the 4-engined G6M "Renzan" and nimbler Yokosuka P1Y "Ginga" more in tone with the previous G3M, the last G4M took part in desperate conversions like a mother plane for the Yokosuka MXY-7 Ohka suicide craft. There was a 1940 heavy fighter derivative, the Mitsubishi G6M1 usable as long-range escort fighter but later converted as a transport. No fully intact G4M survived the war but several airframes were saved from the elements and remained in unrestored state or partial restoration.