Why is the A6M Zero's lack of armor considered such a critical weakness?
Certainly, the A6M was largely unarmored, meaning that .50 caliber rounds from American fighters could penetrate it easily. However, it is worth noting that most American fighters such as P-51, P-47, F4F, and F6F were not protected against .50 caliber fire either, they were only have armor protection from 0.3 cal gun, so if they were to fight one another, the 0.5 bullet would have penetrated their fuselage just fine, no different from A6M case.
On the other hand, A6M also carry 20 mm cannon. Which mean A6M weapon is also more than capable of shot down american fighter like F4F and F6F with 2-3 hit on target.
Given this, why is the Zero's lack of armor emphasized so heavily when compared to Hellcat and Wildcat?. If both sides possessed weapons capable of penetrating each other's aircraft and inflicting catastrophic damage, what practical difference did the presence or absence of armor make in actual combat?. Why aircraft like Splitfire, P-51 were not considered light armored like Zero?, even though their inlight engine were vulnerable and they aren't protected from 0.5 cal either.
It is not accurate. American aircraft were specifically designed to withstand hits from .50 caliber rounds. Their self-sealing fuel tanks were standardized to resist not only penetration (self-seal) but also the hydrodynamic effect (water hammer) produced by .50 caliber AP projectiles. By contrast, contemporary self-sealing tank designs in other nations typically offered protection only against .30 caliber fire, falling well short of the American standard.
Newer U.S. designs incorporated further refinements. The F6F Hellcat, for example, suspended its fuel tanks in a hammock of nonmetallic material that isolated shockwaves and prevented incendiary components detonating nearby from compromising the tank. As for armor plating, it is true that most American armor was not intended to stop .50 caliber AP at close range; however, when accounting for the bulkheads situated in front of the armor plates, .50 caliber rounds still had great difficulty penetrating the cockpits of U.S. Navy fighters. (Further details can be found in the U.S. Naval Institute Proceedings article "The Story of the Self-Sealing Tank," February 1946.)
In contrast, Japanese research into protected fuel tanks began relatively late and relied heavily on materials provided by Germany. The IJAAF was the first to adopt self-sealing tanks, but these early versions were only effective against .30 caliber fire. According to a TAIC report, they proved very poor against U.S. .50 caliber hits. Moreover, Japanese fuel tanks had a tendency to dissolve when using fuel produced in Southeast Asia—a problem the Americans had long solved but one that Japanese planners neglected.
American tests revealed that the M1 incendiary round was sufficient to deal with replicas of Japanese fuel tanks, whereas the M8 API round was required to reliably defeat German tanks. As a result, most M8 API ammunition was shipped to the European Theater, while the Pacific Theater continued using the early belt sequence of AP/AP/I/I/T well into 1945. Aces like Gregory Boyington even devised custom belt sequences composed almost entirely of M1 incendiaries.
Later in the war, Japanese tanks saw increased protection. Extra layers of rubber were added, and in some cases carbon tetrachloride was incorporated into internal layers for fire suppression. These enhancements came at the cost of greatly increased weight and reduced fuel capacity, but they did offer improved resistance against M1 incendiaries, making Japanese aircraft noticeably harder to ignite.
The well-known lack of protection on the A6M Zero must be understood within the context of the South Pacific theater. The Japanese often exploited the Zero's exceptional range, but without self-sealing tanks, a single bullet could drain all the fuel, dramatically reducing the chance of survival. The psychological impact of a burning Zero was also enormous for both sides: witnessing a Zero engulfed in flames, with fire trailing thirty feet behind the cockpit as the pilot was cooked inside, was deeply shocking.
Weapon range played an equally critical role. While the Zero's 20 mm cannons were highly effective, their effective range was very short, and most of the time only the 7.7 mm machine guns actually struck the target. Even when 20 mm rounds hit, they often merely caused a U.S. Navy fighter to trail smoke; the aircraft could frequently still return to base. There were documented instances of an F4F absorbing 21 hits from a Zero's 20 mm cannons and survived. Meanwhile, American pilots could engage and destroy a Zero with .50 caliber fire from 400 yards away. Admittedly, there were cases where a Zero absorbed a tremendous number of .50 caliber hits without going down, but the probability of such survival was low. It should be noted, however, that the Zero was built as a carrier fighter and possessed a strong structure in static terms (though not dynamically, as its aileron flutter speed was low). Unlike the Bf 109, I have not seen instances of a Zero's wings snapping off in gun cam footages. But because the Zero lacked cockpit armor and fuel tank protection, its structural strength was rendered largely useless.
