Legendary Japanese fighter aircraft of World War II. Built in several versions ranging from A6M1 to A6M8, usually with several subversions. Technical descriptions to be found elsewhere in the net.
In short: The A6M Zero was a dogfighter par excellence. Very manoeuverable with an excellent climb rate and range (flight time up to 10 hours!). When brought into combat it outclassed its opponents with ease.
Strange at it seems this superiority was the highway to Japans defeat.
A Japanese pilot considered himself as righteous Samurai warrior, mastering his plane and being second to none. The aircraft therefore had to be a purely offensive weapon, armour and self sealing tanks being a contradiction in terms. In prewar opinion even a parachute or assistance from a fellow pilot weren't needed. In Japanese eyes skill, courage and self confidence of the pilot were the counting factors. Getting shot at was the fate of a pilot in error. In consequence the A6M Zero was built for maximum agility, but with its 925 hp motor acceptable performance could only be achieved by extremely lightweight construction.
The Allies in general especially the USA thought contrary. The pilot was the most important factor (the plane being replaced easily). So though armour and self sealing tanks made the F4F-4 more sluggish, a bullet riddled plane with an intact motor brought its pilot home.
In the battle of Guadalcanal these differences proved crucical.
As bullet resistance wasn't the strongpoint of a Zero it could shed a wing or disintegrate altogether. Also the lack of self sealing tanks made it flame easily. The worst point being the lack of armour. A single stray bullet could result in the loss of plane and man.
In US fighter units the earlier unpleasant experiences with the Zero had led to a change in tactics. No dogfight, no looping, no single action. Flown in pairs each plane could protect the other (in a maneuver called "Thach weave" the Japanese plane following one plane automatically got into gun range of the other). In an attack a single pass - preferably from above - was flown; if the enemy wasn't hit another chance was sought elsewhere.
In the outcome the question was not who shot down more, but how many pilots survived to fight another day (aircraft could be replaced). This difference was blatantly unfavourable for the Japanese. The number of experienced veteran pilots who had survived the battle of Midway (200 plus went down with their carriers) had diminished considerably, leaving replacements who had been taken prematurely from training. Of these another sizeable part had already been replaced with even less experienced ones. And so on. Step by step pilot quality went down and accordingly losses mounted. In 1944 the Japanese Naval air arm had ceased to be a serious threat.
In the meantime Kawanishi had its N1K1 Shiden (US code name George), Mitsubishi its JM1 Raiden (US code name Jack) in the pipeline, the former being a converted floatplane. Due to the success of the Zero both designs had not been given highest priority and furthermore they were plagued with engine and other problems. When these new types finally appeared in1944 they were too few in numbers and skilled pilots scarce.
So the Zero soldiered on. Despite constant adaptions to the needs of war - getting heavier and heavier without the necessary horsepower - it always remained second best. In the battle of the Philippine Sea in June 1944 they fell in hundreds. Outnumbered and outclassed the latest variants of the Zero mostly were relegated to Kamikaze duties.
Conclusion: The horrendous losses the Zero suffered weren't the fault of the airplane design as such. But being constructed to an outdated - ancient - fighting philosophy its shortcomings were soon revealed. Hadn't there been such spectacular success in the beginning, the Japanese procurement department and aircraft manufacturers would have sought for an replacement earlier. But this is said with today's hindsight.