Essential Question:

Why didn’t the Japanese A6M Zero have armor and self-sealing fuel tanks?

Much has been said about the Zero’s lack of survivability features, however, most evaluations fail to elucidate the underlying reasons for the Zero not having cockpit armor or self-sealing fuel tanks until the development of the later models.  While indeed, the lack of such features was a serious drawback for the Zero, aviation historian Osamu Tagaya notes that the reasons are often misconstrued by westerners. Rather than being a design oversight, the real reasons for the Zero’s lack of protective features stem from operational philosophies & contemporary attitudes, lack of experience and false conclusions, organizational deficiencies, technological limitations, and finally, psychological and cultural values (Mikesh, 1994, p. 103).

Operational Philosophies, Contemporary Attitudes, Lack of Experience, & False Conclusions

We must understand that in the mid-1930s, neither aircraft designers nor air force officers foresaw the need for self-sealing fuel tanks or armor in aircraft at the time.  In fact, none of the Zero’s contemporaries in the late-1930s, such as the Wildcat, Hurricane, Spitfire, or Bf-109E, initially had sealing tanks or armor either. The change in attitudes in the West was not due to someone’s farsightedness, but rather the harsh realities of combat during the Battle of Britain.  Such features didn’t become standard until the latter half of 1940. Around the same time, and into 1941, U.S. aircraft began having these features installed. Unfortunately, Japan did not heed the lessons that western nations learned in the Battle of Britain and instead drew the wrong conclusions from the Second Sino-Japanese War where they developed a sense of arrogance and superiority given the weak nature of the air opposition in the skies over China.  While the Japanese experience in China did see some combat units request protective features, it was not until the stiff opposition during the Guadalcanal campaign that Japan felt the urgency. It wasn’t until late-1943 that the Zero began having a level of protection that U.S. aircraft already had by mid-1942. By then, the advantage had been hopelessly lost (Mikesh, 1994, p. 104 – 106).

In Jiro Horikoshi’s words (regarding adding armor to the Model 52c AKA A6M5c):

The most significant request was bulletproofing, a feature which had not even been mentioned in the Zero’s initial planning requirements.  Over the years, the lack of bulletproofing has frequently been mentioned as a weak point of the Zero. The reason for this shortcoming was that the aircraft could not afford the additional weight necessary for bulletproofing, given the requirements stipulated with respect to heavy armament, long range capability, and maneuverability.  These items took priority over anything else, and since we did not have reliable high-power engines, bulletproofing was sacrificed. Japanese pilots of those days had a feeling similar to that which must have been experienced by skillful samurai who single handedly fought many well-protected enemies. This attitude on the part of the pilots accelerated the general trend of assigning a low priority to bulletproofing.  Certainly, if one type of aircraft demonstrated overwhelming offensive ability, this in itself could become a major defensive force. But as our opponents’ offensive abilities approached or even exceeded our own, an unskilled pilot or one who was outnumbered needed the additional protection of bulletproofing (Horikoshi, 1981, p. 144).

While aviation is not my field of expertise, it is important to put the concept of aircraft armor into context. Aircraft are not armored like tanks or fortresses. What is gained in weight is lost in speed and agility. According to Mark Peattie (2001), designing a combat aircraft is a trade-off between weight, speed, ceiling, range, maneuverability, armor, armament, and any number of other variables (p. 91). Cockpit armor is largely a pilot survival feature. Remember that the Zero was designed as a fighter plane and not a ground attack aircraft. Ground attack aircraft like the Il-2 Sturmovik or the modern A-10 Thunderbolt II are designed to fly low and slow and are expected to be targeted by enemy anti-aircraft fire. Hence, they are built with armor, redundant systems, and are generally very rugged in construction. The Zero, and many fighter aircraft including modern ones, favor speed, and agility. True, many Allied fighter planes did incorporate some armor for survivability, but their ability to withstand punishment and return to base was also the result of their very rugged designs. There are historical instances of aircraft taking seemingly ridiculous amounts of damage and still being able to bring the pilot back safely. Grumman Aircraft Corporation was famously known as the “Grumman Iron Works” for consistently designing very rugged and reliable planes.

Organizational Deficiencies & Technological Limitations

The design requirements for the Zero set forth by the Navy were seemingly contradictory. Horikoshi and his team worked tirelessly to create a lightweight fighter that possessed impressive range and maneuverability. However, sacrifices had to be made in several areas. While a superb design, the Zero possessed many single-point failure points where structural failure would result in the complete destruction of the aircraft. Furthermore, while the Zero’s climb rate was unprecedented at the time, its dive speed was relatively slow, a problem that would put it at a disadvantage later in the Pacific War with the introduction of heavier and faster Allied fighters. The legendary maneuverability of the Zero was only notable in slow-turning dogfights below 4,500 meters (15,000 feet). Pilots noted that at its maximum speed of 288 knots at 4,500 meters, the ailerons stiffened and the plane became extremely sluggish (Peattie, 2001, p. 92).

Regarding the industrial capabilities in Japan, we must remember that in contrast to the technologically advanced Japan that we see today, the Japan of the 1930s and 40s was still an agrarian and light-industrial society that was being ruled from the top down by a totalitarian regime.  Japan emerged from feudalism in 1868, and in less than 100 years, they had bridged the technological gap, but only due to the imposition of industrialization from the government, and only in certain areas. While Japan could produce some internationally competitive products, the standard of living and economic infrastructure still lagged significantly behind the West.  Tagaya compares Japan at the time to the Soviet Union or many present-day Third World countries. As a result of Japan’s industrial limitations, they could not produce a high-grade rubber of consistent quality necessary for self-sealing tanks which delayed their development (Mikesh, 1994, p. 106).

Horikoshi further attributes the problems with the Zero mainly to its “underpowered engine.”  He mentions that in Japan, it was standard procedure to prioritize certain design elements. Thus, “it was natural for a fighter not to be bulletproofed” (Horikoshi, 1981, p. 151).  He goes on to say:

Priorities varied between different aircraft types.  For example, a bomber could not maneuver to avoid the bullets of an enemy fighter in daytime combat, regardless of top speed.  Consequently, bulletproofing should have been a high priority item for a bomber. In the case of a fighter, the pilot’s skill and the performance of the airplane could compensate for the lack of bulletproofing to some extent.  In short, bulletproofing was a low priority for a fighter, but it became more important as pilot skill decreased and as the number of enemy fighters increased (p. 151).

Finally, Horikoshi mentions a memo from the Navy Aeronautics HQ written 1 year and 5 months after the start of the war which mentioned the need for bulletproofing in the future.  However, he says that:

In those days, the consensus still seemed to be that the advantages of improved maneuverability and increased offensive firepower with a lighter aircraft made it inadvisable to weigh a fighter down with bulletproofing.  In the future, bulletproofing would be clearly necessary, but for the present its absence resulted from our efforts to strengthen offensive firepower. As a matter of fact, only when the United States stepped up the counterattack and introduced new, powerful fighters in overwhelming numbers did bulletproofing become essential (p. 151).

Psychological & Cultural Values

Japanese cultural values may also explain why the Japanese took longer to address the problem of aircraft protection.  The samurai psyche still pervaded Japanese society, particularly the military, which demanded an acceptance of an honorable death.  While irrational by today’s Japanese standards, anything that hinted at trying to save one’s skin, such as armor plating, was seen as cowardly.  Additionally, Japanese aviators often demanded the most out of their aircraft, thus any additional weight that would reduce its performance was dismissed.  The underlying attitude was that such protective features were luxuries rather than necessities. Only after the wholesale attrition of the pilots did they finally see that living to fight another day was more important in modern warfare than dying an honorable death (Mikesh, 1994, p. 106).


In summation, according to Horikoshi, why did the Zero not have armor and self-sealing tanks?

  1. It was never mentioned in the initial design requirements.  (indeed, he never once brings it up earlier in the book when he is discussing the design of the Zero).
  2. Weight restrictions meant the prioritization of armament, range, and maneuverability for the fighter.
  3. Lack of a high-powered engine meant weight had to be saved.
  4. Military ethos assigned a low priority to armor.
  5. Lack of credible enemy air threats early on meant armor was not thought to be needed until later on.

As can be seen, the design requirements of the Zero favored creating a fighter plane with excellent handling characteristics.

This is actually a good lesson in the evaluation of historical evidence.  We do have Horikoshi’s memoir to go off of here, so that provides us with a strong primary source, albeit, published 30 years after the fact.  We should be careful of using the benefit of hindsight to project our evaluation onto the decisions that were initially made. This is known as hindsight bias.  We should also be careful of creating a negative proof here. Just because there is no evidence that the Zero’s designers or the navy considered adding armor or self-sealing tanks, does not mean that they never did.  Rather, we could say that we have found a low correlation with the fact that they did not consider adding such features to the initial design. Furthermore, it is difficult to establish this beyond any reasonable doubt because valid empirical proof would require the establishment of possibility and probability.  The evidence must be relevant and in the affirmative. We cannot just say that X was possibly the case, rather we must also establish that it probably was and present relevant evidence. Horikoshi does state that weight restrictions meant the prioritization of armament, range, and maneuverability, but we have not established that any one of those was the most probable factor on why they left out armor and self-sealing tanks.  Many other components of the Zero were sacrificed to meet those requirements and we also see that there was an entire ethos embodied in the design philosophy.


Horikoshi, J. (1981). Eagles of Mitsubishi. (S. Shindo & H.N. Wantiez, Trans.). Seattle, WA: University of Washington Press. (Original work published 1970)

Mikesh, R.C. (1994). Zero: Combat & Development History of Japan’s Legendary Mitsubishi A6M Zero Fighter. Osceola, WI: Motorbooks International.

Peattie, M.R. (2001). Sunburst: The Rise of Japanese Naval Air Power 1909-1941. Annapolis, MD: Naval Institute Press.