Model 11 and 21 from Mitsubishi
The First Operational Zeros
François P. WEILL

Though only two Models were registered officially in the IJNAF nomenclature, both Model 11’s and Model 21’s appeared with differences from batch to batch. Here is an attempt to clarify these differences.

As usual were the Historian will be satisfied, the modeler isn’t. He needs more information on the specific machine he intents to model … To a point he is generally frustrated in his attempt to copy the reality. His two main concerns, the conformity of his model in shape and the so controversial subject (as far as Japanese planes are concerned) of camouflage will be covered here with all the natural reserves concerning the accuracy of the finish used on these peculiar aircraft as the point is still under debate.

From the A6M1 12 Shi prototype, the new model A6M2 Model 11, was more than a re-motorized variant. The shape of the fuselage was altered and the tail planes were moved outside the aerodynamic effects of the wings by rising them slightly. The fin and rudder area was augmented. It seems that the three first airframes though motorized by the Nakajima Sakae 12 of 940 HP instead of the Mitsubishi Zuisei 13 and – like the last Model 12 Shi – using a three blade constant speed propeller retained the original combined arrangement as far as the oil cooler and carburetor intake were concerned. Thereafter, the arrangement became the standard one that could be observed on all Sakae 12 equipped Reisen: A chin scoop for the carburetor intake and a separate oil cooler intake just behind. As none of the three first airframes were ever used operationally, this is of a very marginal importance.

It must however be understood that all Model 11’s were in fact pre-series planes and particularly for airframes up to # 47, subject to small alterations not even clearly mentioned in the surviving documents. The most notable of these was the chin carburetor scoop shape which was altered during early Model 11 production run to get its definitive shape. Early Models had a distinctive shape of chin scoop mimicking whistling lips (often referred to as pinched air scoop) but the number of concerned airframes and the exact repartition of this early feature by serial number is still unknown (so watch carefully the photos of the plane you are actually modeling). Zero interim manual of 1940 says the definitive shape was applicable from N° 67 aircraft on but photographic evidences denied that all but a few 12th Ku. Machines had the early scoops.

Another early feature of the Model 11 which was to stay up to Zero airframe # 47 was the entirely glazed end piece of the canopy. As one of the particularities of the Reisen was to have an easily removable rear fuselage (both for transport and maintenance) it was found that this glazed end was prone to damage and thereafter this part was entirely metallic. Thus the Zero got its definitive canopy.

Up to airframe # 34, the exhaust tubes exited from the fourth cowl flap, thereafter they were given their definitive arrangement, exiting from the fifth cowl flap, each side of the oil cooler intake.

Otherwise, the Model 11 fuselage was similar to the better known Mitsubishi built Model 21.

The wings didn’t have the foldable tips of the later Model 21 (a feature which was sufficiently important to justify a modification in the aircraft designation). But as long the wing tips were not folded, it is impossible to notice the presence or the absence of this feature.

More important, the ailerons of the Model 11 were totally unbalanced. It means that no mass balances as carried on early Model 21’s are to be seen on a Model 11

The wing cannons had a specific outlet, much larger than the muzzle: a square indent in the wing leading edges with rounded corners. A feature that outlived the Model 11 as we will see, as the elliptical shape of the cockpit fresh air intake on the right wing root.

It should be noticed that even after successful carrier qualification, the wingspan (12 m) of the Model 11 was considered too much a liability in the heat of combat, considering the standard width of the IJN carriers. A fact which led to the Model 21 folding wingtips but also to the fact that all Model 11’s were not considered as carrier fighters in the official nomenclature but to take the Japanese designation as "base defense fighters" and were never used operationally from carriers. A consequence of this fact for the modeler being the absence of the arresting hook on all operational Model 11’s, another the absence of the DF loop under the rear cockpit canopy fairing.

Model 21

It must be very well understood that, originally, the early Model 21’s had all the specific external features of late Model 11’s. There were only two differences:

  1. The already mentioned manually folding wingtips
  2. The presence of a mass balance under each aileron.

This last feature – on the contrary to some already published sources – is a trade mark of all early Model 21’s up to airframe # 326, but around 80 airframes from airframe # 127 modified by IJN Air Arsenal with a complicated device linking a Flettner to the flaps to avoid overcompensation at slow speed (this device will be described later in the text.

In fact the inability of the Reisen to maintain a high roll rate at high speed despite an otherwise exceptional maneuverability (for a fighter of his generation) was realized early and the search for a cure led to the adoption of external mass balances from the first Model 21.

However modifications will appear without alteration of the designation.

  1. From the 127th airframe and for about 80 airframes the Navy Air Arsenal of Yokosuka developed an aerodynamic compensation for the aileron. This device was a Flettner (in flight movable tab) linked by a complicated rod and articulation system to the flaps of the aircraft. It helped the aileron control which was extremely stiff at high speed to operate properly. As over control was unsuitable at low speed (moreover for a carrier born aircraft) this device was automatically neutralized when the flaps were lowered 30° or more. Unfortunately, the combination of a better high speed roll rate with an insufficiently strong rear spar led to the destruction of two Model 21 Zeros, one causing the death of the pilot. From there on the reart spar was beefed up on the assembly line and the Yokosuka Air Arsenal device eliminated, the mass balances being re-instated. It should be noticed that the same device was re-(instated on Model 22 without causing wing failure. I’m almost certain that the fact that this device was not designed nor approved by Mitsubishi team was instrumental in its withdrawal, despite that the real problem was a combination of a weak rear spar and the augmented efforts created by the higher roll rate.
  2. From airframe # 227, the shape of the cockpit fresh air intake on the right wing root was altered to its definitive shape: a small rectangular hole instead of the older and bigger elliptical shape.
  3. From airframe # 326, a final alteration appeared concerning the wing cannon outlets which became small, round and flush with the wing leading edges. It should be noticed that his modification was apparently the only one which led to a retrofit to all first line planes as attested by photos of Zeros from the "Hawaiian Operations" having mass balanced ailerons and (at least for some) elliptical cockpit fresh air intakes but flush wing cannons outlets.
  4. From the same airframe, the mass balances were eliminated, a new static compensation device being introduced consisting in a mass buried in the aileron leading edge in front of the articulation axle. A cleaner device, aerodynamically speaking, but not much more efficient than the mass balances. Thus, creating the definitive Mitsubishi built Model 21. This model will later be the base from which Nakajima Hikoki K.K. developed its own Model 21 production (see the corresponding article).


We are now entering a much more speculative field. What follows should be considered as my personal interpretation of known facts.

Model 11 camouflage

The Reisen was the first IJNAF "modern" plane to enter service with a factory finish which included an "offensive" (air to air) camouflage. It is almost certain that the Model 11’s employed in China were subjected to tests. The rear part of the fuselage (with a straight vertical delimitation but not corresponding to the rear fuselage separation line), the tail planes and the external two third of each wing (it seems from the photos that the delimitation was less sharp there) seems to be painted in a lighter color than the rest of the airframe which appears darker and glossier. The only feature that will be carried out on all Zeros was the glossy black (in fact a gray-black or even a blue-black) cowling.

One of our friend, Asuza Ono, thinks even the fuselage Hinomaru presented a darker half corresponding to the two tone delimitation. A fact that – at least with the photos that are available to me – is not so evident (IMHO, it is more relevant of an optical trick).

What were these two colors is not substantiated by any material evidence.

My personal guess is that originally the Zeros were to be painted in the light blue gray or gray green already in IJNAF inventory (probably a matte or semi-matte paint), but the successful experiment already conducted on A5M4 Model 4 carrier fighters with a high gloss slightly amber varnish (the real "Ameiro" ??) directly applied on the natural metal of these fighters (thus giving them a slightly amber metallic tan appearance) as a corrosion proof sealant led the IJNAF authorities to the idea of using it as a complementary protection on, or within the "gray" paint to see if a more resistant finish was obtained, despite the slight change in general color toward a greenish gray with some tan in it and the glossy appearance that resulted from this change. The test was conducted on the 12th and 14th Ku. Model 11’s during their stay in China by covering only a part of each airframe with this new shade which appears glossier and darker on B&W photos.

The exact way the new shade was obtained is difficult to assess. What we know is that the resulting gray-green was generalized thereafter on Model 21’s (and may be on late Model 11’s too). We know also that on Model 21’s no coat of varnish proper was ever used on the airframe but a glossy paint. My personal opinion is that the "definitive" version of this finish was the result of a mix between the pigments of the original matte or semi-matte paint with the amber varnish, then sprayed on the airframes. But, if our friend Asuza is right with the fuselage Hinomaru, it is entirely conceivable that the amber varnish was an over spray on the original "gray" paint (which may be the explanation for the earlier theory of a varnish sprayed as an overcoat on Zeros).

Model 21 camouflage

At the time Model 21’s were produced the "black" cowl + high gloss medium gray green (with a slight tan value in it) was of general use. As Mitsubishi ended Model 21 production in June 1942, it is obvious that all Mitsubishi built Model 21’s were factory finished this way. But, without any doubt, makeshift camouflages appeared in the Solomons from September 1942 (refer to the Nakajima built article for more details on these camouflages). Of course too the dark green coat, mandatory after around June 1943 was applied on surviving Mitsubishi built Model 21’s. But it is almost sure that the under surface of these planes remained glossy gray green. Aircraft used in training units seems to have remained unchanged at least until June 43 onwards but for certain alteration on a few planes that exchanged their all black cowlings to an American like anti dazzle panel on the cowl upper surface of the cowling only. I have a lot of doubts concerning the use of orange yellow on single seat training Zeros but as this shade is not discernible on B&W photos …

The internal finish, propeller, eventual IFF stripes and factory markings

All internal surfaces were coated with green or blue tinted Aotake varnish giving the surface a metallic green or blue appearance.

The cockpit was finished with Mitsubishi interior green (near to FS 34151 but darker) applied on the original Aotake coat. It seems that the interior of the cowling was finished like the exterior.

The fuselage under the canopy was finished the same color as the cowling.

On all Mitsubishi built Zero 21’s, the propeller complied with the early war regulations, being polished natural metal on the front of the blades and spinner and black on the rear of the blades. At 5 cm from the tip of each blade two parallel red bands, 5 cm wide, separated by 5 cm were applied.

Other factory markings were similar to Nakajima built models (see the related article) but the identification plate (always carried on a gray-green zone and of a different format).

All yellow IFF stripes when applicable (from November-December 1942) where field applied (as Mitsubishi production terminated earlier than the use of these identification markings).

The six Hinomaru, as factory applied were brim less.

Modeler’s corner

I will only refer to 1/72nd kits here. I’m not a quarter inch modeler. But it is obvious from the fact the best A6M2 kits available being Hasegawa’s that moist of what is indicated for 1:72nd scale is almost similar to the corresponding 1:48th series of the same manufacturer.

Model 11 kit is IMHO the worst of the series. In fact it is a re-boxed Model 21 kit with accurate decals for a Model 11 without any specific parts.

The assembly instructions are poor as the specific differences with the Model 21 and between Model 11’s are completely neglected. The only differences in the assembly sequence are limited to the emplacement of the exhaust which are referred to as if all Model 11’s had these parts exiting from the fourth cowl flap (you now know it is not true) and the absence of aileron horn balances. On the decoration guide, the indicated colors are not clearly indicated and the outer wing panels are incorrectly treated entirely in the darker color and despite the absence of a specific canopy part, all the Model 11"s represented are of the all glazed canopy variant (no guarantee that all the decorations were related to this variant). The probable presence of some Model 11’s having the "whistling lip" carburetor intake has been completely neglected. Beware of the fact that the wings carry all the aileron balance system used from Model 11 up to Model 22. So for a correct Model 11 putty the lines defining the flettners and keep the fixed tabs. On the 1/72nd scale kits, the fresh air intake for the cockpit is all but omitted… So be prepared to drill an elliptical one. Of course, the cannon outlets are of the definitive Model 21 shape. So you have to drill indent square ones with rounded corners. If required by the plane you model, you may have to modify the carburetor intake to the whistling lip variant.

Valid for all the Hasegawa Zero kits, the use of corresponding Eduard photo-etched details is highly recommended.

Model 21 may be assembled almost straight from the box if an airframe superior to # XXX (but for the internal details). The only alteration will concern the suppression of the Flettners engraved lines on the wings.

Not so for an earlier plane. If any plane engaged in anger seems to have been at least retrofitted with the late model cannon outlets, the other alteration of the wing appearance depicted for Model 11 are applicable here (some training machines even retained the original cannon outlets), according to the description given in the main text. For the 80 or so machines as transformed by Yokosuka Air Arsenal (that ended their career in training duties without being brought back to their original configuration) remember to keep the Flettners engraving and to eliminate the fixed tabs.

Finally, notice that a lot of Model 21’s used by shore based units saw their radio equipment (including the DF loop) eliminated because of unreliability. This is almost constant in the Solomons. It seems also that the same planes were often deprived of their arresting hook.

I won’t give you a coverage of Mitsubishi built Model 21 unit markings as this subject will necessitate a entirely specific article.

I hope the present work will help…

Stay tuned for a revised edition of my article published in the Asahi Journal about the Nakajima built Model 21’s.

© François P. WEILL