It seems like the zero post was popular, so here's more! There were a ton of variants of the Zero fighter: (in chronological order)
1. A6M1 type 0 prototype. Completed in 1939, equipped with a Mitsubishi Zuisei 13 cylinder engine with a 2 bladed prop, making 780hp.
2. A6M2 type 0 model 11. Switched to Nakajima Sakae 12 cylinder, making 940 hp. They were so impressed that they had 15 built and shipped to Manchuria, where they decimated the Russian built Polikarpov I-16's, aka the "flying squirrels". The Japanese were impressed and officially put the model 11 into full production. At this point we still didn't believe the Japs could build a plane like this....
3. A6M2 type 0 model 21. Introduced folding wingtips to make carrier storage easier.
4. A6M3 type o model 32. In 1942, Nakajima introduced the Sakae 21 engine, which used a 2 speed supercharger, increasing power to 1130hp. The new engine was larger so they moved it backwards towards the cockpit, decreasing the size of the main fuel tank a bit. They also got rid of the folding wingtips, and squeezed in more ammo for the 20 mm cannons. Only 343 of this type were built.
5. A6M3 type o model 22. Same as model 32 but with a belly mounted drop tank and wind tanks for more range, and they got the folding wing tips again !?? Some of these were fitted with a 30mm cannon over the previous 20mm.
6. A6M4 Type o model 41. These attempted to use a turbo-supercharged Sakae engine, but apparently they didn't have enough alloy to make the complex manifolds the engine required. A few of them burned up, so they gave up on this version.
7. A6M5 type o model 52. Considered the best, most effective Zero, this one was made to go up against the kick ass Hellcat and Corsair. Thicker, stronger wings for faster diving and redesigned exhaust improved performance all around. Also had some armor around the cockpit, and a cockpit fire extinguisher built-in.
8. A6M6c type o model 53c. Introduced self sealing wing tanks and a Nakajima Sakae 31A engine with water-methanol boost.
9. A6M7 type o model 63. Decked out for Kamikaze attacks, probably with more bombs and fuel. Its kind of fucked up they had an official "model" specifically designed to get blown up! These probably didn't have the fire extinguisher.....
10. A6M8 type o model 64. The final version. Now powered by a Mitsubishi Kinsei 62 engine making 1560 hp. The engine was so mush larger than the previous one that they got rid of two machine guns that had previously been mounted in the nose coweling. They also added another drop tank, and generally beefed up the entire plane to hold up to the increased power. Unfortunately, only 2 were built. That was it, war over. [youtube=http://www.youtube.com/watch?feature=player_detailpage&v=SpJyaT_0gh0]