There was a time in the U.S. where every Japanese plane was a Zero. Well, we all know that that isn't true, but we also know that the Zero is called by many types, models names etc, hopefully this article will go a ways in helping clear things up as to how to identify each type of Zero.
First, a bit of background on the Zero. Development on the A6M1 "Reisen" began in 1937 with the issuance of the 12-Shi Carrier Fighter specification as a replacement for the A5M "Claude". The first flight of the Zero occurred April 1st, 1939 and was piloted by civilian pilot Katsuzo Shima (a Mitsubishi test pilot).
The A6M1 is easily identifiable with it's two bladed propeller (switched to a three bladed prop later), also there was a carburetor air scoop located on the top (or possibly the bottom) of the cowling. This aircraft was powered by the Zuisei 13 engine which was greatly under-powered. The A6M1 failed its preliminary carrier trials in September of 1939 and the second prototype blew up in mid-air (March of 1939) killing it's Navy test pilot.
In the third prototype a Nakajima Sakae 12 engine was installed. The third prototype with redesigned wings and strengthened wing spars and the Nakajima Sakae 12 engine was designated the A6M2 type 0 Ship-Based fighter Model 11 or Zero-sen ("Zeke" to the allies). This model was also called A6M2a (not officially as the Japanese designation system really didn't have any sub lettering system and only the designation A6M2 appeared on the aircraft dataplates). Sixty-four Model 11's were produced and were mainly used in the Sino-Japanese war.
As the success of the Japanese Army mounted in China in 1940, a grim reality set in for the Japanese Navy bombers. The war had moved so far inland (to Chunking) that the Navy's G3M2 "Nell" bombers were ranging past the ability of their fighter cover to escort them. Once they arrived on target, they would be deluged with Russian built I-15s, I-16s and US built Hawk III's . The Chinese pilots would wait at altitude and then make diving passes at the unprotected bombers.
Once the Zero arrived, these tactics changed. When the air raid sirens blew, the Chinese would man their planes and head to hide behind some nearby mountains waiting for the Japanese fighters to leave the area. On September 13th the Japanese sent thirteen Zeros on a mission to Chunking. As usual when the bombers left, so did the Zeros. A type 98 (probably a Ki-36) reconnaissance plane was also sent on this mission. The reconnaissance aircraft remained over the target at high altitude awaiting the return of the Chinese aircraft. The reconnaissance pilot reported the returning Chinese aircraft and the Zeros turned to do battle. The twenty-seven Chinese aircraft lasted less than 10 minutes in the fight before being completely destroyed, without a single Zero lost. This battle also produced the first Zero-Sen "ace", Petty Officer Koshiro Yamashita, who shot down five of the Russian-built Chinese fighters. Needless to say, the first combat of the Zero was an overwhelming success and the legend of the Zero began.
The A6M2b or A6M2 Model 21 was the main early production model of the Zero. The main difference between the Model 21 and the Model 11 was folding wingtips. After the 127th aircraft a mass balance weight was added under the ailerons and the trim tab was removed.
The A6M3 Model 32 (allied code name "Hap","Hamp" and finally Zeke 32)was the next variant produced. The Model 32 is easily identifiable based on it's clipped wings. The clipped wings were implemented to improve the high-altitude and climb rate of the Zero.
The A6M3 Model 22 was the next major revision of the Zero. The Model 22 went back to the basic airframe of the Model 21 with the new Sakae 21 engine. With the size of the new engine, the cowl shape was changed and the gun troughs were removed.
The A6M3a Model 22a added a rudder trim tab and a pair of long barreled type 99Mk. 2 Model 3 cannons in the wings.
The A6M4 was a modified A6M2 with a "turbosupercharged" Sakae engine. Very little is known about this variant, other than it was never put into production.
The A6M5 Model 52 brought several interesting changes to the Zero. The wings were shortened 19.69 inches. The most distinctive difference however was the addition of individual exhaust stacks on the Sakae 21 engine and the openings that were cut in the cowl for the stacks to protrude through. The model 52 also brought the first self-sealing fuel tanks, and armor that would be seen on the Zero.
There were three additional models of the type 52, the Model 52a (Ko) changed the type of cannon that was used in the wing guns. The Model 52b (Otsu) added bullet proof glass behind the windscreen and replaced one of the 7.7mm fuselage mounted machine guns with a 13mm machine gun (and likewise the look of the cowl changed as well with an enlarged gun opening). The Model 52c (Hei) added two type 3 13mm machine guns outboard of the two 20mm wing cannons, as well as removing the remaining 7.7mm fuselage mounted gun (leaving the fuselage with only a single gun port opening). The model 52c was also equipped to carry air-to-air rockets.
With the new allied planes coming of age, the Zero was changed again to fit another roll, that of a bomber. The A6M7 Model 62 included a bomb rack to replace the centerline drop tank, two additional 40 gallon wing tanks and thicker skin on the tail in order help sustain higher dive speeds.
The final version of the Zero, which was called the "the best Zero model" by the Japanese test pilots who flew it, was the A6M8c. This aircraft had a much larger cowl to accommodate the Kinsei 62 engine. This led to the deletion of all fuselage mounted guns. The aircraft never made it into production as the war ended before the first model made it off the line. The production model would have been known as the A6M8 Model 64.
As you can see, the Zero went through many different configurations. While it was quite a successful aircraft early in the war, the basic design was never changed enough to keep up with the F4U Corsair or the F6F Hellcat. While the Zero could out turn and out maneuver these aircraft, it was still significantly slower and lacked sufficient firepower to be a real threat late in the war.
Additional notes from Sander Kingsepp
I read your Japanese Aircraft Primer article and I would like to add some comments on the first combat of the Zero, based on Takayuki Amekura’s article “Reisen Jukei uijin” published in the Rekishi to Tabi magazine (Akita Shoten 8/1988 special issue).
First, the recce plane involved was more likely a C5M1 (Babs). While Amekura didn’t specify the type he referred to it as a Rikutei Type 98 which in IJNAF parlance usually meant the well-known Kamikaze, later widely used as a pathfinder for Zeroes. Moreover, according to Amekura the C5M1 pilot spotted the returning CAF fighters on September 12,. i.e. already the day before. There was a similar recce plane present on the next day but it did not accompany the fighters until Chunking but returned to its base around 1310. As the Japanese already knew about the Chinese stratagem, they simply flew until Lanshi and then doubled back as appointed before the take-off. The pilot who spotted the Chinese first was PO2/c Yoshiro Oki.
Amekura’s article also contains some interesting details about Model 11’s teething troubles, how many of them were initially sent to Hankow and a fascinating excerpt from the battle diary of Toraichi Takatsuka.
1) Japanese Aircraft of the Pacific War by Rene' J Francillon, Putnam Aeronautical Books, 1970 Pg 364
2) Zero, Combat & Development. History of Japan's Legendary Mitsubishi A6M Zero Fighter, Robert C.Mikesh, Pub Motorbooks International. Pg 85
3) Mitsubishi A6M1/2/-2N Zero-Sen in Japanese Naval Air Service by Richard Bueshel, Pub. Schiffer Military History Books. Pg 8
4) Eagles of Mitsubishi, The Story of the Zero Fighter by Jiro Horikoshi, University of Washington Press 1970. Pg 99
5) Aero Detail #7, Mitsubishi A6M Zero Fighter, pg. 72