The Imperial Japanese Navy’s A6M2-K Zero Trainer or Rei-Sen Ren-Sen

By Rob Graham

For years, publications have shown photos of the A6M2-K Zero Trainer, which has always been said to be an A6M2 that was modified by adding a rear seat and cockpit. A story once put forth mentioned the A6M2-K was constructed using obsolete and / or reconditioned parts. Close inspection reveals the A6M2-K was not likely based on an A6M2 at all, and few photographs show evidence of reconditioned or obsolete parts. In the photo collections, it is apparent upon close inspection that the A6M2-K was very likely an aircraft that was built using A6M3 model 22 or A6M5 model 52 (later airframes) parts with various modifications to adapt the Sakae12 engine. This document bears the ever-mounting evidence for this case.

Shortly before WWII, the Imperial Japanese navy was phasing out the veteran Type 96 Carrier Fighter (Kyu Roku Kan Sen, or "Claude"). This aircraft was the world's first all-metal monoplane carrier fighter and was designated the A5M. Many of these were being converted for the training role at Hitachi [and Sasebo?]. New Japanese naval fighter pilots were honing their dogfighting skills in the modified two-seat aircraft. The Japanese navy fighter pilots were "cutting their teeth" in a then-great aircraft to become part of an elite group of fighter pilots who would fly the A6M Type Zero Carrier Fighter (Rei Sen, or "Zeke").

When World War II broke out, Zero pilots were truly in a league of their own, quite a few of them having become seasoned veterans in China. However, as the war raged on, losses of both man and machine became dearer. The Japanese navy needed to train pilots to fly the newer Zeros. In January of 1943, the Japanese navy's 21^st Naval Air Depot (or Sasebo Naval Arsenal), whose production was augmented by Hitachi beginning in May of 1944, built the Type 0 Trainer Fighter. Using Mitsubishi A6M3 Model 22 airframes, a seat and controls were added under a full canopy behind the original cockpit, which now was rendered permanently open. Fins were added to the fuselage sides, in front of and just above the stabilizers, to aid with spin recovery. Sakae 12 engines and A6M2 cowls were mounted to longer engine mounts and covered with lengthened access panels between the cowl and firewall. The design was a success. Some A6M5 airframes were later modified and used as well; quite possibly most, or all 279, of Hitachi's production was based on A6M5 airframes.

Zero Fighter airframes existed in several evolutionary iterations, with variations in firewall location, wingspan, and so on. The latest research shows the Zero Trainer airframes existed in a few iterations as well, though photos indicate later style fuselages (with further-aft firewall) normally associated with Sakae 21 powered aircraft. Wings seem to vary, with earlier airframes having the longer wingspan of the A6M2, and later airframes with the shorter span and round tips of the A6M5. Many other parts such as spinners and rudders seem to vary. No photos have been published detailing the interior of the rear cockpit.

Research indicates the likelihood the planes were made from parts stocks from what was being built on the Fighter assembly lines as they were assembled. Here's the breakout as seen in the photos:

Theory: Zero Trainers were assembled from all-new components and sub-assemblies, with the 21^st Naval Air Depot at Sasebo using the A6M3 Model 22 followed by A6M5 Model 52, and Hitachi using A6M5 Model 52.

Mitsubishi had been building the A6M3 Fighter for more than six months prior to Sasebo's A6M2-K Trainer production, which ran during the last year of Nakajima’s A6M2 production. No photos show the further forward firewall of the A6M2 on a Zero Trainer, thus the Model 21 airframe was likely never used. Since the firewall seems to always be in the further aft location of the Model 22 and later airframes, and the planes feature the shorter cowl of the A6M2 model 21, the early Zero Trainers were probably A6M3 model 22 airframes with Sakae 12 engines and cowls.

Production schedules shown in Appendices F, G, and H of Zero: Japan's Legendary Fighter by Robert C. Mikesh shows A6M2-K production and parts availability never happened during Mitsubishi's A6M2 production, though it did happen during Nakajima's A6M2 production. However, since no A6M2-K is shown to have an A6M2 airframe, it appears the first year of A6M2-K production may have involved Mitsubishi airframes exclusively.

Several A6M5 airframes outfitted as A6M2-K aircraft are seen in photographs, thus indicating there were more than just the seven Hitachi prototypes. See page 68 of Zero: Japan's Legendary Fighter by Robert C. Mikesh and the bottom two pictures on page 68 of Aero Detail #7, Mitsubishi A6M Zero Fighter by Shigeru Nohara. Note the aircraft at the bottom of the page has the features that identify it as a late production A6M2-K (extra large spinner, large diameter propeller, A6M5 airframe, Sakae 12 engine and cowl), likely built after June of 1944, hence probably built by Hitachi. Note the Nakajima-style camouflage demarcation as well; these indications seem to point toward a Hitachi / Nakajima production partnership. Another A6M5 based A6M2-K, aircraft GeN-19, can be seen in the top photo on page 221 of Model Art #510. The caption seems to say adjacent aircraft, GeN-37, is an A6M5 as well. The drawing below the photo of GeN-37 shows how Shigeru Nohara has mistakenly shifted the cockpit and windscreen forward, close to the firewall; this is not correct. In many of Nohara’s newer A6M2-K drawings, the airframe is drawn this way.

Another view of an A6M5 airframe aircraft can be seen at the bottom of page 81 of Famous Airplanes of the World #5. The aircraft's aileron inner edge (oriented to the navigation light and wing top access panel) is clearly in the further outboard location of the A6M5 aircraft. For comparison to an A6M3 Model 22 or A6M2 Model 21 style aircraft, see the photo at the bottom of page 78 of the same publication.

Some questions seem to remain unanswered:

First, did the A6M2-K airframe shift from A6M3 Model 22 style to A6M5 Model 52 style by date of manufacture, or was it the difference between Sasebo and Hitachi production? There is a lack of evidence either way, though more photos may some day surface and clarify the situation.

Second, was it indeed the A6M3 Model 22 airframe or an A6M2 model 21 with a further aft firewall? We would need to see if the wings were equipped with the outer fuel tanks.

What's that door on the left side of the fuselage? Some drawings (pages 80 and 117 in Maru Mechanic #08308-12) show a door on the aft part of the fuselage. No photos seem to show this door, though it could be where the target-tug winch was accessed or it may be just another fallacy. If anyone knows, please share!

For the modeler...

Interior details may be based on information found in Green Arrow’s publication, Illustrated Zero Fighter, and other photo resources. Since some model kits and conversions have been offered which essentially duplicate the front cockpit (right down to the machine guns) for the instructor's (rear) cockpit, scratch-built interior details seem the only way to go. For 1/48 modelers, Squadron has made available some vac canopies from Falcon of Australia; and Create 301 of Japan made a conversion kit, though that’s very rare. A good choice would involve either an A6M3 model 22 or an A6M5 model 52 and a cowl and engine from an A6M2 model 21. 1/72 modelers have had available kits from Gartex and AML. The AML kit is relatively easy to find, though it would be better as a source of parts to modify an A6M3 Model 22 for the serious modeler.

Color should be Toh-Oh-Shoku, a Pale Yellow Orange (H4), Munsell 10YR 7/7, FS 23434 with a black cowl.

This is the left profile of Tsu-403. Note the added metal strip behind the access panel, between the cowl and the firewall. When the original panel was shifted forward to fill in behind the smaller Sakae 12 cowl (with the leading edge in the same location as the original), there was a gap by the firewall that needed to be filled. A strip of sheet metal (seen in red circle) was riveted to the trailing edge of the access panel to accomplish this.

Note aircraft "Ke-428" aileron and shadow of the wing (circled in yellow) shows it is a "Mk 5" airframe. The firewall is also further aft as well, though the cowl has the A6M2 cowl and chin carburetor scoop (circled in blue). Note the circled "4" on the rudder, the Nakajima scheme with white Hinomaru surrounds and angled upper and lower demarcation line (which has the externally adjusted trim tab of the early A6M2, circled in green). Notice the spinner is the larger type, circled in brown. See that the pilot’s retractable boarding step of aircraft number "Ke-453" has been added for the rear cockpit, on the right side (circled in purple). While it is not obvious in these two pictures, the access panels aft of the cowl were likely modified panels, lengthened with strips of sheet aluminum to the trailing edge of the standard A6M5 panels. This is obvious in some pictures of these planes.

With these two pictures, we can see a "Mk 5" airframe and a "Mk 3" airframe, "Mk2" cowls, engines, and rudders, very late style propellers and spinners, and other telltale signs of seemingly random and variegated hardware. Color schemes seem almost every bit as random, as well. This random mix may indicate use of reconditioned components and sub-assemblies.

Interior details for the modeler:

While there are no definite pictures or diagrams to date, some details may be gleaned through study of the aircraft's design. Study has shown the left side of the aircraft's cockpit probably looked quite different in the back than in the front.

Note the left console is virtually not necessary. Note the throttle, rudder pedals, and pitch control quadrant and the control stick are both present, though reconfigured to accomodate linkage forward, to the front cockpit. The seats and rear control panel have been omitted from this drawing to allow better viewing of the various features. The control panel was likely the same as the front panel, the seat was also likely similar, though it is doubtful the bulkhead behind the rear seat resembled that of the front cockpit, and there was almost certainly no need for the rear seat to raise and lower, so it probably was fastened to the subfloor. More information is being gathered for the right side of the cockpit, as that is primarily radio gear, but details are less sketchy than previously shown.

Conclusion:

The A6M2-K has not appeared in any photograph as an A6M2, but the fact remains the A6M2-K short designation was somewhat of a misnomer for an aircraft that actually was based on A6M3s and A6M5s. It's too hard to nail down the specifics about A6M2-K production and parts sources, and the relationships between Nakajima / Mitsubishi (Zero Fighters) and Hitachi / Sasebo Naval Arsenal (Zero Trainers). This remains a tantalizing and open case.

Bibliography:

Mitsubishi A6M1/2/-2N Zero-Sen, Richard M. Bueschel, Schiffer, 1995, ISBN 0-88740-754-4, page 27

Zero: Japan's Legendary Fighter by Robert C. Mikesh, Motorbook International, 1994, ISBN 0-87938-915-X, pages 68 and 94 and pages 124-126

Illustrated Zero Fighter by Shigeru Nohara, Green Arrow Publishing, ISBN 4-7663-3178-8, pages 20 and 235

Aero Detail #7, Mitsubishi A6M Zero Fighter, Shigeru Nohara, 1993, ISBN 4-499-22608-2, pages 68 and 75

Squadron / Signal #59 - A6M Zero in Action, Shigeru Nohara, 1983, ISBN 0-89747-141-5, page 45

Japanese Aircraft of the Pacific War, Rene J. Francillon, 1970, ISBN 0-87021-313-X, page 397

Model Art #510 Japanese Naval Fighter Camo and Markings Special, Various authors, 1998, ISBN T1108734032706?, pages 220 and 221

Famous Airplanes of the World - A6M models 11-21, #5, 1987, pages 78 and 81.

Acknowledgements go to all the researchers and historians who have brought this information to be published, including (but not limited at all to) the late Richard Bueschel, Robert Mikesh, Shigeru Nohara, Jim Lansdale, Jim Long, Jim Broshot, and many others. A special thanks goes to Greg Springer.

© 1999, 2000 Rob Graham