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Some Thoughts on the Japanese Naval Airforce Land Based Bomber Program

by Dwight Cox

Click here for a larger image
A G4M "Betty" bomber carrying a Baka bomb

Much criticism has been heaped the G3M and G4M series bombers of the JNAF, but how much is deserved?   The ‘Nell’ and the ‘Betty’ are derided by historians for their inability to withstand gunfire from Allied fighters. A closer look shows some deeper fundamental mistakes by the JNAF.

In 1933 Admiral Yamamoto convinced the JNAF to adopt a policy of land based long range bombers to engage enemy fleets far out at sea.  Three years later the Mitsubishi G3M1a went into service as one of the most advanced long range bombers of any air force in the world. Routine missions in China with a combat radius approximately 1200 miles were flown.  Due to heavier then expected Chinese opposition losses were heavy.  This led to two consequences, the G3Ms defensive firepower was given a modest upgrade, and far more importantly the G4M program was delayed for one year while a small group of officers insisted on employing the G4M as a ‘Convoy Wing Tip Fighter’.  This caused a crucial one year loss of production. In all fairness the USAF’ YB-40 program tried do the same thing and met with as little success as the Japanese did.  The Americans’ huge industrial base allowed for a certain leeway in pursuing dead end ideas, and the remote control chin turret was soon included on late model B-17Fs and the follow on B-17G.  But the twenty times smaller industrial base of Imperial Japan did not permit the make up of the production deficit.

Admiral Yamamoto’s vision was vindicated on 10 Dec 1941 with the sinking of the HMS Prince of Wales and Repulse.  After this it was all down hill for the G4M.   To be sure the G4M had its good points, the MK4A Kinsei 1530hp engines compared favorably with the GR-1820 1280hp Wright Cyclone engines having only a slightly inferior performance above twenty five thousand feet.  The defensive armament of the ‘Betty’ in its later models became quite formidable with four twenty mm cannons.   However its propensity for catching fire was only partially ameliorated, in part because of the lack of two additional engines.

This brings us to the JNAFs second major error. Mitsubishi had requested permission to upgrade the design to four engines, but the JNAF refused. At the time Nakajima was trying modify the American Douglas DC4-E airliner to a long range bomber.  This aircraft was a first class turkey and was rejected by the airlines as uneconomical and by Douglas as an unworkable design.  There are those who maintain that the US Government knew that Japanese Navy wanted to convert the airliner to a bomber and wanted to tie up a major portion its aircraft industry.  Be that as it may, the JNAF ignored the old proverb ‘A Bird in the Hand is Worth Two in the Bush’ and suffered accordingly. The Nakajima G5N Shinzan never entered service and the four prototypes finished the war as transports. Two additional engines on the G4M would have allowed the designers to install adequate self-sealing tanks, fire extinguishers, and armor plating without sacrificing the long range desired by the JNAF. This in all likelihood would have turned a very good aircraft into an out standing one.  One only has to look at the Kawanishi H8K ‘Emily’ Flying Boat or the Avro Lancaster’ transition from the Manchester with its failure prone Rolls Royce Vulture engines.


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