Mitsubishi A6M1: Returning to Zero

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The A6M’s legend started in May 1937 with a requirement for a fighter that would replace the A5M. After almost 2 years of development the first A6M1 was completed in March 1939 after which the first prototype A6M2 with the new Sakae 12 (Ha-35-12) was finished in May 1939 with delivery to the navy happening in December 1939. This suggestion is for the A6M1 (S/N 201 & 202) that started the journey that ended with the A6M8 model 64.

1:1 scale replica of the A6M1


The design requirements for the aircraft that would result in the A6M1 were send out on the 19th of May 1937 to both Nakajima and Mitsubishi. Based on the ongoin and planned future when it came to the plans of Japan in Asia the Japanese navy wanted to replace the A5M that was currently in service. This new design was created by looking at the performance and development of European aircraft and then requestion even higher performance from the new design. The request was as follows:

  1. Role: As an intercepter it can destroy incoming bombers, as an escort fighter it should be better in air to air combat then the enemy interceptors.
  2. Speed: The design should hit 500km/h @ 4000m or more
  3. Climb rate: reach 3000m in 3 min 30 sec
  4. Cruising range: 1 hour 10 min - 1 hour 30 min @ 3000m or 1 hour 30 min - 2 hours @ 3000m with a drop tank.
  5. Takeoff distance: 70m or less with a 48km/h headwind
  6. Landing speed: 170km/h or slower
  7. Glide rate: 210-240m/min
  8. Be as good or better then the A5M when it comes to air to air combat
  9. Armament: 2x 20mm cannons & 2x 7.7mm machine guns
  10. Bombs: 2x 30kg bombs or 1x 60kg bomb
  11. Radio: Type 96 No.1 Aircraft Radio, Type 1 No.3 Wireless Direction Finder
  12. Equipment: Oxygen system, a Fire extinguisher, Night light, Basic instruments

Following these requirements a study group was assembled on the 17th of January 1938 in Yokosuba, at this meeting Major Genda gave a detailed account about the lessons that he learned on the battlefield over China and how these lessons should be incorperated into the new design. Following debates based on Major Genda’s statements the Navy restated that the design requirements needed to be met.
According to a representative from Nakajima these requirements couldn’t be met and the new fighter aircraft “cannot be built” before withdrawing from the competition. Leaving only Mitsubishi in the race, after development of the aircraft the first prototype was completed on the 18th of March 1939. Because the Nagoya factory didn’t have a testing runway, the freshly completed A6M1 was ordered to be moved to Kagamigahara airfield. As such the brand new fighter ended up being moved per Ox cart, much to the frustration of the Mitsubishi design team.
Following re-assembly, some minor repairs and ground tests at Kagamigahara, the A6M1 took to the skies on the 1st of April 1939. After landing some problems were found: the left wheel brake didn’t work, the engine oil overheated and there were some vibration issues. However due to the minor nature of these issues the test was considered a great success.
After more intense test flights, on the 14th of September 1939 the Japanese navy designated the new aircraft as the 12th Year Type Experimental Carrier-Based Fighter. The second prototype was delivered on the 18th of October 1940 while being accepted on the 25th. The third prototype got the new Nakajima Sakae 12 engine and was renamed to the A6M2.
Not everything went perfect with the A6M1 however as during testing with the 2nd prototype on the 11th of March 1940 the aircraft suddenly disintegrated, as test pilot Okuyama died during the accident and the aircraft was destroyed a thorough investigation was conducted. Using wind tunnels tests and investigations of the wreckage the naval authorities concluded that rudder balance had failed following either a landing or another type of shock what in turn caused the airframe to shake itself apart in the dive. This conclusion was supported by the Mitsubishi engineers and considered a small blemish on the development on a new aircraft.
The first A6M1 was most likely scrapped at a certain point but at the Gifu-Kakamigahara Air and Space Museum there is a 1:1 scale model of the A6M1, bringing the first zero (design) back to where it all began.


A6M1 S/N 201 being constructed with S/N 202 in the background


Due to the worse performance when compared to it’s full production model, the A6M1 would be a great fit for the A5M4 to A6M2-N gap or depending on the enemy team it could also fit between the A6M2-N and the A6M2 Model 11. At the same time it would also show the start of the famous airframe in the same way that the recently added Bf 109 C-1 does.


A6M1 with exposed engine


General characteristics:

  • Crew: 1 (Pilot)
  • Length: 8.79m
  • Width: 12m
  • Height: 3.49m
  • Wing Surface: 22.438m2
  • Empty weight: 1,652 kg
  • Full weight: 2,343 kg
  • Powerplant: Mitsubishi Zuisei 13 (Ha-31)
  • Engine output: 780hp @ 0m
    • 875hp @ 3700m
  • Engine kg/hp: 2.68kg/hp


  • Maximum speed: 509 km/h (207 knots)
  • Operational range: 1.2-1.5 flight hours
  • Climb rate: 5000m in 7 min 15 seconds

Standard Armament:

  • 2x Type 99 No.1 Mk.2 20mm cannons (120 rounds)
  • 2x Type 97 7.7mm Machine Guns (1360 rounds)
  • 2x Type 97 No.6 Model 1 Mod. 1 60 kg GPHE bombs


  • No self sealing fuel tanks
  • Twin bladed propellor
  • Drop Tank



A6M1 S/N 201 being constructed


A6M1 S/N 201 being moved to Kakamigahara Airfield



D51 第二次大戦 日本海軍機写真集 エアワールド1994年3月号別冊 送料込
三菱重工業名古屋航空機製作所で組み立てられる十二…:零式艦上戦闘機 写真特集:時事ドットコム
零式艦上戦闘機の誕生(零戦 3)
1 April 1939 | This Day in Aviation
Aircraft Photo of No Reg | Mitsubishi A6M1 Reisen (Zero) | #276095
『零戦の日 今日は何の日?』
11-1-10-2 1式空3号無線帰投方位測定機 - 日本帝国陸海軍無線開発史



A friend is asking, but do we know it was armed with 20mm’s? At all. Or was this based on the A6M1 Prototype 2?

Every written source for the aircraft states that they were armed with the 20’s and 7.7’s, I can’t really say much more then that honestly. There (to the best of my knowledge) aren’t really any pictures of the A6M1’s after the IJN recieved them, outside of 1 picture of A6M1 No.2 after the accident but that one is rather useless when it comes to your question.


Good write-up! I appreciate the brief history/development.

Unfortunately with how overtiered Japanese planes are, it would probably be at 3.0/3.3

The picture you posted the one above
There are 0 holes in the picture I posted, for the 20mm cannon mounts.

Alright, so chances are neither the A6M1 had 20mm cannons. Given Google Translate and DEEPL(The most current advanced and accurate translator). I think it’s implied that they were added on later in the 3rd design->A6M2. It wasn’t equipped on the A6M1 at all.

Seems like the translator was getting a little confused about what they meant but I think it’s implied so chances are the A6M2 proto was given the cannons. Although in a game this is fairly obvious as it seems like the wings were expanded in the A6M2 design to accommodate the 20mm cannons.
Which is the part where the Translator struggled to interpret it.

A prime example of this is this picture of the A6M1 from the front
This in one of the sources shows that there were no cannon mounts on this variant and that’s due to the wings being fatter and not expanded. This was changed in Prototype 3 which accommodated the larger fuel tanks but also the 20mm cannons. So if anything it would be 1.3 or 1.7

Possibly lower, since the more you dive into the iceberg, the more and more it seems that this variant only had 2 nose mounted 7.7’s MG’s.


If it was intended to have the 20 mm cannons I’d rather it have it

I don’t. Since it wasn’t equipped with them it makes no sense to add a pseudo-fictional aircraft. Every picture shows it wasn’t. So it really shouldn’t. It also takes the light away from the Ki-43’s and Ki-44’s. Cause everyone will attempt to gobble the Zero up.

Aside from that, the 3rd “Prototype” which was the first for the A6M2. Was the one that used the Cannons. It’s simply a translation error and or poor writing from the sites. So unless we get someone fluent in both English and Japanese. Would be difficult to confirm anything.
Not 1 translator but several. Multiple would better put things into concrete if they give similar answers.

If you look at aircraft No.2 in the 2nd picture you can see that the areas where the 20’s would go. So even if in theory they weren’t mounted post delivery they had the ability for it.
For comparison, a later A6M with the same panels removed.

The wings were completely unchanged between the A6M1’s and A6M2’s, the tail section is the only part of the air frame that was changed.

I’m pretty sure I see what you are reading in the sources but you simple are reading it incorrectly. In this source 『零戦の日 今日は何の日?』 that you are quoting, it’s simple stating that the wings are thicker due to the extra fuel and the new 20’s.

The book I am using, D51 第二次大戦 日本海軍機写真集 エアワールド1994年3月号別冊 送料込, is in Japanese and I got a Japanese person to help me with it. That book states 20’s being present in the A6M1. Ignoring that there is also the old forum suggestion that was made by Aizenns, who also is Japanese, that quotes multiple Japanese sources that states that the 20’s are a thing.

Putting all that together, I really don’t see any reason why the 20’s would be hypothetical due to the lack of pictures of them being mounted in the aircraft.


I’m not sure if the armaments were installed in the A6M1 prototypes, but they definitely were built with the provisions to install them. In the book「軍用機開発物語」there are several photos of A6M1 fuselage and wings under construction, and the mounting positions for the 20mm MGs and 7.7mm MGs are obvious.

And in the “A6M1 Flutter Experiment” document on the Japan Aeronautic Association’s website, you can see the A6M1 wing structure design with the 20mm MG.

Furthermore, at this time, the 20mm MG was not yet called Type 99, it was the Type E 20mm Fixed MG. E (恵) for “Erikon” (Oerlikon). The designation Type 99 was applied in 12/1941.

If A6M1 was not outfitted with its weapons, I personally don’t think that it matters. The provisions were there, and it is not even close to the only aircraft in this game fitted with weapons that were not yet used.


Someone did fine this though.

The image you posted is the Akutan Zero. Had to reverse the image search which is an A6M2(one in a game that’s captured is that exact aircraft), not an A6M1. Although I looked deeper you’re right, it did have the mounting. The cannons were not mounted so personally better to just have the A6M not start with the cannons but if they’re equipped its BR gets increased.

Now this isn’t necessarily the most reliable however there’s a lot of backup to back this claim/theory. Which is a bunch of text and images related to the original A6M1 blueprints. Or at least a recreation of them with slight creative liberties to the illustration. Which is what I provided below. This confirms some of what I believe which is that the A6M1 and A6M2 have a lot of differences. From the flight stick to other components in the wings. Including the size of the wing spar and wing span. Similar to how the Ki-43 I can get 12.7, stick with 7.7, or swap to 12.7.
Aside from that, the A6M1, irl had larger fuel tanks but was shrank to accommodate the 20mm cannons this was before they started to mount the exterior fuel tank.

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Two blades is all I need to slice the enemy plane to bits. +1


From further research, the cannons were not fitted during flight tests. At least not the earlier ones. It seems like once they got to the predecessor that became the A6M2, they were fitted.
So if anything Gaijin just gotta do the Ki-43 treatment again. There seems to be a lot of Japanese aircraft that would rely on this standard if they were added.