Re-evaluating the A6M Zero – The Armored Zeros

A6M5b & c variants (The armored Zeros)

Over the course of its production the Zero was gradually upgraded to include additional features.  It was not until the introduction of the A6M5b & c variants (in Japanese known as otsu 乙 & hei 丙 ), that protection for the pilot began to be implemented.  The b variant added a 1.75in panel of bullet-resistant glass behind the windshield. Additionally, one of the 7.7mm MGs was replaced with a 13mm MG. This was the first change in the Zero’s armament since the prototype.  470 of the b variants were produced (Mikesh, 1994, p. 90).

The c variant continued to upgrade the plane’s firepower and protection.  For firepower, two 13mm MGs were added to the wing armament outboard of the 20mm cannons.  To compensate for the increase in weight, the remaining 7.7mm MG was removed. Under-wing racks were also installed to allow the aircraft to carry rockets or bombs.  For protection, an armored plate was added behind the seat and additional panels of bullet-resistant glass were added in the canopy frame behind the pilot’s head.

In order to maintain the aircraft’s center-of-gravity, the fuel load was redistributed by adding a 37 gallon self-sealing tank in the mid-fuselage and reducing each of the main wing and outer wing tanks to 41 gallons and 6.5 gallons, respectively.  The drop tank was also reduced to a 79 gallon capacity. As a result of these changes, the c variant was 13 knots slower and 600 pounds heavier than the base model.

By this time, chief designer Jiro Horikoshi was occupied with designing the A7M Reppu and further modifications to the Zero was conducted under the supervision of engineer Eitaro Sano.  While there was some discussion in installing the new Kinsei 62 engine which would have provided a 250 hp increase, the navy did not allow it and instead advised the use of water-methanol injection for increased power.  However, further developments were delayed and the c variant remained with the Sakae 21 engine. Production began in September of 1944 (Mikesh, 1994, p. 91 – 92).

It was not until November of 1944 that the water-injected Sakae 31a engine was installed and the A6M6c variant was created.  This version included additional self-sealing fuel tanks, but the armament remained the same. The design was not adopted into service because it failed to meet expectations.  The water-methanol metering system failed frequently during testing and the new engine actually had reduced power due to its modifications. Only one aircraft was produced and the project was cancelled (Mikesh, 1994, p. 92).

What was it all for?

I previously mentioned the concept behind aircraft armor, but it bears reiteration. Remember that aviation history is not really my area of interest and I am more or less drawing some general conclusions. First of all, it is impractical to armor an aircraft like it is a battleship or a tank because the thing will never get off the ground.  Assuming it did, it would handle like a flying elephant. I have only seen an elephant fly in Walt Disney movies and that one time when U.S. Army Special Forces delivered an elephant to the Montagnards in Vietnam in 1968.  But that is beside the point! Even armored aircraft are still relatively thin-skinned due to most of the armor being focused around the cockpit and critical systems. In planes like the Fairchild Republic A-10 Thunderbolt II, even systems that are not armored have redundancies to ensure that they can be operated if their primary means of operation fail.  The WWII equivalent is probably something like the Soviet IL-2 Sturmovik. However, these are ground-attack aircraft and it is anticipated that they will interact with targets on the ground that find their presence unwelcome. Even fighter planes that were known to take numerous hits and keep on flying were not armored to the nth degree.  Although some did possess armor, the key feature was that they were very sturdy and well-built.

I think a lot of people misconstrue armor as imparting some kind of invulnerability. Indeed, there is something to be said for the ability to absorb hits (i.e. staying power), but remember that we are talking about vehicles here, not castles or bank vaults.  The enemy may eventually shoot something at you that, while it may not penetrate, can still cause serious damage. What you gain in armor, you lose in mobility. The Tiger was a superbly armored tank, but you could only drive it 70 miles across country before you needed to gas it up.  Not to mention that later Allied guns that could penetrate its armor. Aircraft, especially fighters, rely primarily on their mobility and speed to survive. Armor in an aircraft is basically meant to provide Mr. Pilot with some degree of protection from having his insides become decoration for the interior of the aircraft.  Either that or allow him time to bail out of what is left of his aircraft while it plunges to the ground in a fiery ball of doom. That being said, Japanese pilots often did not fly with their parachutes, because it added extra weight and it would have brought grave dishonor upon the Emperor if they did not die in a blaze of glory.  In any case, as people like Mikesh have noted, the addition of armor and self-sealing tanks to the Zero was too little, too late in coming. We’ve already looked at the factors for why that is, but in the end, it does not seem like the addition of such features to the Zero without a concomitant increase in engine power drastically improved its effectiveness so late in the war.


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

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