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The Evolution of the Japanese Army Steel Helmet (1918-1945) Revised and Expanded Version

Article about: The Evolution of the Japanese Army Steel Helmet (1918-1945) Prolog During the Russo-Japanese War, the army received a letter dated 28th April 1905 from a private inventor, who had the idea t

  1. #31


    1939: Other users of the type 90 helmet (War Correspondents and Export)

    The Army design helmets were strictly military and were not available to civilians, but there were a handful of cases where Type 90s were produced without the Army star insignia in front for use outside the Japanese Army.

    One of these exceptions was helmets for war correspondents requested by Asahi Newspaper and Domei News Agency issued in 1939.

    A letter from Asahi to the Minister of the Army, dated June 17, 1939 explains, “In light of the fact that our correspondents, photographers and messengers, who have nobly given their lives to the current China Incident have all fallen due to being shot in the head…” and requested permission to procure 100 helmets for the use by such staff. In August, the other major media company, Domei News Agency made a similar request for its 50 front line newspapermen. The Army’s production order for these helmets specifies omission of the Star Insignia.

    Also, in the early days of the Type 90 helmet, frequent requisitions for Army helmets without insignia can be found coming from an organization named “The Taihei Association (World Peace Association泰平組合)”. The irony of the name is that they were an exporter of Japanese surplus weapons.

    After the Russo-Japanese War, Japan’s active weapons development rendered many weapons obsolete and the trading houses Mitsui, Okura and Takada were competing with each other in buying them up and exporting them to countries such as China, England and Russia. When Lt. General Nambu of the Type 14 pistol fame noticed the three companies bidding against each other only to benefit the foreign buyers, he suggested that they should rather team up than compete, which took the form of the Taihei Association.

    They changed names in 1939 April to Showa Trading when Takada dropped out and was replaced by Mitsubishi.
    They are shown to have shipped regular steel versions of the type 90 prototype samples to Chiang Kai-shek in 1930, samples to Mexico in 1935 and 1939, to Peru in 1936 and 1,000 helmets to Mongolia in 1940. These were normally supplied with other weapons. These helmets, too, were devoid of any star insignia.

    1932-1938: The Bullet-proof Type 98 Helmet

    Readers may recall that when Kobe Steel got involved in steel helmets back in 1931, it was also given the personal armor project. The Type 38 rifle, modified to 7.7mm caliber was the special test weapon for that project. One may also recall that the development objective of the Type 90 helmet was to make it as light as possible “even if the protective attributes had to be compromised within reason”. As would be expected, the wearability of the helmet had its cost in lives during the Manchurian Incident when taking fortified enemy positions required close range fighting, typically exposing combat engineers. So with such users in mind, a “bullet proof” helmet was included in the personal armor program and studies began in May of 1932.

    Additional Armor Plating Option

    They decided to pursue two options for adding armor plating to a standard type 90. One option was the so-called “Hachimaki” or head band option, adding a ring of extra armor. The other style was to add a plate to the entire front of the helmet. Prototypes of these two styles were placed with Kobe Steel Company in June 1932, and in August, after testing, the decision was reached that the addition of frontal armor was the preferred solution. A further prototype order was placed with Japan Special Steel Company, on 10th September 1932, which was delivered in October. Between November of 1932 and February 1933 a batch of these prototypes went through field evaluations by the infantry school, the engineer school and the 9th Infantry Division. They all gave the thumbs up, so it was decided to seek official type approval for this spec.

    Prototype with Integral Additional Armour

    In addition to the above, in March of 1933, a decision was made to have Japan Special Steel Company do prototyping of a helmet, having a plate thickness of 4mm in front and 1mm in the back, with an angled front design that deflected rounds better. This prototype was delivered in June and was tested at the firing range of the Tokyo arsenal in Koishikawa. This prototype had been made by welding together the front and rear plates of different gauging, but now a modified version, riveting the front and rear together, was to be prototyped, this time at Kobe Steel. This phase 2 prototype was delivered in August of 1933 and tested again at the Koishikawa range. This testing revealed that frontal armor thickness of between 2.5mm and 3mm would sufficiently protect against rifle rounds from a range of 300 meters.

    The next round of prototyping studies were conducted between October 1934 and January 1937 by Kobe Steel, which made 32 prototypes. They experimented using various thicknesses and shapes. This Kobe Steel prototype had a sharper angled front than the type 90 and front armor thickness ranged from 1.2mm to 3.97mm, resulting in a weight range of 945 grams to 3,585 grams.

    It was at this time that trials at the army medical school, infantry school and engineer school established the trade-off relationship between wear comfort and protection. They concluded that although one could not wear anything more than 1kg (what the Type 90 weighed) in weight for prolonged periods, a load up to 3kgs could be tolerated, if for a very limited time.

    In December of 1937 prototypes were now made using 2mm gauge steel in two different designs, one identical to the type 90 and another similar to the German M35 helmet. This meant that the weight would also almost double, now weighing 2 kilograms. However, this allowed the helmet to withstand a direct hit at 500 meters from the 7.7mm round, which would have penetrated a standard type 90 even from 1000 meters away. Both were to have the additional option of 2mm thick detachable front armor plate, weighing 0.8 kilograms,which could be screwed onto the front of the helmet to withstand hits even at 300 meters. These two alternatives were tested at the infantry and engineer schools and resulted in February of 1938 in the decision to go for the type 90 shape with detachable plating in front. Other changes to the type 90 included extending the chin straps by 20 centimeters and using kapok or plant sponge from Japanese gourds for the padding to enhance shock absorption. Final retuning of prototypes was finished in July 1938 and in August, studies were completed and official type approval sought as the type 98 helmet.

    However, despite the Type 98 designation, most army documents referred to it as the Jyu-Tetsubo重鉄帽 (heavy steel helmet). For instance, when the Army’s Close Combat Advisory Commission issued their report on techniques and weapons for assaulting fortified enemy positions in December 1938 it used the term Jyu-Tetsubo. This terminology also remained in use when the Infantry and Engineer Schools also joined these studies from late 1939 and put in their requisitions for these helmets along with the turtle shell armor and all forms of bullet shields, flame throwers and the like.

    However, the Type 98 designation did finally appear in a 1940 dated army document describing the arsenal of close combat hardware (shown below). In comparison with the Type 90, official specs for the Type 98 Tetsu-kabuto are given in this document as follows;

    1. Shape identical to the type 90

    2. Shell thickness increased to 2mm from the 1mm of type 90

    3. Weight increased to approx 2kg from the 1kg of type 90

    4. Option of screwing on additional front armor of 2mm thickness and weighing 0.8kg

    5. Surface finish of type 98 to be matte paint finish

    6. Liner structure to be similar to the type 90, but padding material to be Kapock or Hechima, both plant sponges.

    7. Chin straps extended by 20 cm from the type 90 specs

    8. Although, not mentioned in specs, I think one can expect to find markings of Kobe Steel in the shell, which is the “S” in a diamond.
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  2. #32


    Although as I already mentioned, an army ordinance of 1932 had switched the Japanese name for Steel helmets from “Tetsu-Kabuto” to “Tetsubo” , the official designation for this variant was the 九八式鉄兜,”Type 98 Tetsu-Kabuto”, not Tetsubo. This was probably to underline the positioning of the type 98 as a special weapon for raids, in the same league as the turtle shell body armor developed for assault engineers, not as a piece of uniform like the type 90 helmet. So the Type 90 was a Tetsubo, but Type 98 was a Tetsu-Kabuto.

    The Type 98 was also considered for use by snipers and by sentries besides when attacking enemy bunkers, but they were only issued in extremely low numbers. The soldiers would normally be wearing a Type 90, and will change into Type 98s when they drew special duty or a raiding mission. Issue numbers I typically see in requisitions only range from 10 to 20 units at a time, so they must be extremely rare. So far, I have never seen an original type 98.

    Interestingly I find no mention anywhere whether the Type 98 also came in small and large sizes like the type 90. My guess, however, is that they probably had the large size only, as studies leading up to the Type 98 indicate that there were less head injuries when the helmet was loosely sitting on the head than when firmly held in place, mentioning the common field practice of wearing a “tenugui” under the helmet. This was probably also the reason why they extended the chin straps by 20 cm.

    Another mystery is whether the provision for screwing on an additional armor plate was present at all on the type 98 helmet shell itself or whether such a mechanism was all positioned on the extra armor plating. Though I have combed the archives, nothing that shows drawings has turned up to settle this question of how the additional armor was added to the type 98. However, because the plating was originally conceived as added protection for the Type 90 helmet chances are that they developed it to fit both the Type 90 and Type 98 helmets, which would require the complete fixing mechanism to be on the plate.

    They do not mention the star either, but I feel there is a high probability that it was devoid of insignia, as the star in front would get in the way when you wished to attach the extra front plate. Also they might have needed a quick way to visually tell Type 98 apart from a Type 90, as appearance was otherwise supposed to be identical..

  3. #33


    Development of Helmet Covers for the Type 90 Helmet (1933-1938)

    The wearing of helmets used to be an exception rather than the norm, but as the helmet became a part of the uniform soon after the start of the Manchurian Incident, it became more of a constant presence on the soldier’s head, and with it came the headaches and other discomforts. A problem that required addressing was the heat buildup within the helmet being baked under the sun.

    Some form of heat insulation had to be provided and this led to the Army’s adoption of a cotton padded helmet cover on June 1st, 1938 through Army Ordinance no. 31 (陸達第31号). Though that was the timing it was officially adopted and entered regular supply, units in China had been wearing them as prototype items since the summer of 1933 when the first batch of 3,100 sets arrived at the headquarters of the Army stationed in China

    Army Ordinance 31 and attached helmet cover drawing shown below along with an original example of this first model.
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    Last edited by nick komiya; 10-24-2015 at 07:50 PM.

  4. #34


    The troops in China tried them out that summer of 1933 from July 5th until September 15th and the official evaluation report was sent to the Minister of the Army, Sadao Araki in the name of the commander of the troops in China, Lt. General Kotaro Nakamura.

    This report attests to the effectiveness of the cover in preventing heat buildup inside the helmet, saying that even after a 3 hour march under a sweltering sun the surface of the helmet under the cover showed only moderate heat and did not cause discomfort to the wearer. It also mentions three other side benefits. Firstly, that it contributes to concealment from the enemy by not reflecting the sun or light at night. Secondly that it prevented the steel helmet from damaging their guns by working as a cushion. Thirdly, its noise muffling qualities ensured stealth in night time operations, and also prevented wind noise made by the vent holes of the helmet in strong wind, which interfered with communication.

    However, Nakamura also pointed out some improvements that required to be made to the prototype covers. He mentions that the covers were too heavy and caused excessive fatigue in extended wear, and that the base cloth needed to be waterproof to prevent it from sucking up water and becoming even heavier during rain. Lastly, he says the covers are too small for the corresponding helmet size and required to be more generous in fit and that the draw string should be made to be tied at the middle of the visor.

    Between the summers of 1934 and 1935, helmet covers became part of a large scale tropical uniform development program, and like the last big tropical uniform development tests of 1921, it took place in Taiwan. In July 1934 the 2nd Taiwan Infantry Regiment received 160 samples each of three different helmet covers for testing.

    The difference between the three was the heat insulation material used. Type A (甲) used cotton and weighed 100 grams, Type B (乙) used plant sponge from the Japanese gourd and weighed 155 grams and Type C (丙) used felt and weighed in heaviest at 175 grams. When the temperature inside the helmet was compared after a march in the sun, the felt model proved between one and two degrees centigrade cooler than the cotton version with the plant sponge version scoring in the middle. Despite the better cooling effect of the felt, the light weight and pliable, easy to handle properties of cotton made it the choice of the troops in the jungle. The other tropical items tested at the same time went through another round of tests in 1937 and 1938, but the helmet cover did not join that round as the matter was already settled.

    It is not clear on what basis the covers were supplied after the summer of 1935 when the test in Taiwan ended and before they got standardized in 1938, but even before the second year of testing in Taiwan was over, a large shipment going out this time to the Kwantung Army and the 4th Infantry division, in June of 1935, included 5,000 covers along with 5,500 helmets, rounding out a cycle of testing that started out in China in 1933 and travelled to Taiwan in 1934 and now to the troops in the northern part of the continent.

    The original specs called for pure cotton as padding material, but spec descriptions for the official introduction on 1st June 1938 already said “pure cotton or similar material”. This alternative material was called スフ(Sufu)、which was actually an acronym made out of two English words, Staple Fiber, which is none other than rayon, itself a word made up combining Ray (as in the sun shine) and Cotton. So the helmet covers made with Rayon instead of pure cotton have the Sufu stamp inside.

    And in early 1943 the so-called second model helmet cover appeared, which had the lower rim reinforced with a tape of cotton, similar to the helmet chin strap material. This was to prevent the rim of the helmet from cutting through the helmet cover.
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    Last edited by nick komiya; 10-24-2015 at 07:52 PM.

  5. #35


    Finally a navy version for comparison.
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  6. #36


    As a sideline, apart from the development of the cover, the Army’s Scientific Research Institute had been conducting studies on the shell itself to find means of achieving better heat insulation for the helmet, which led to the granting of a patent on July 2, 1938 titled “Heat proofing of steel helmets (patent no.125576)”. The three researchers who applied for the patent found out that the rougher the inner surface of the helmet, the more intense the buildup of heat became inside, due to the larger surface area the roughness brought. For them the key was to obtain a smoother surface within the top part of the inner dome, and the patented idea consisted of plating the inner top surface of the helmet, for instance with chrome and to coat the lower part with saw dust or silk fiber mixed in shellac or other adhesive solutions. Their experiments showed that this method lowered the internal temperature by as much as 10 degrees centigrade more than in an untreated helmet. As the difference achieved in the helmet cover testing in Taiwan was a mere 1-2 degrees, 10 degrees is indeed a massive improvement factor, but one can easily imagine, that such an exotic method did not lend itself to mass production in terms of production time and cost.

    I hope you enjoyed this one.

  7. #37


    Very neat thread! Currently I have a vet bringback Type 99 from the Aleutian Islands and a Type 2 Paratrooper rifle. Looking to get a HINOMARU YOSEGAKI, a officer or NCO sword and a good helmet. Any recommendations on a specific type or branch of service to look for in a helmet?

  8. #38


    Fantastic thread. A great addition to the sticky list!!
    Thank You Nick
    Semper Fi

  9. #39


    Excellent thread, Nick! I recommend you for "Life Membership" based on the quality and depth of your scholarly research.

    Oh .... wait a minute ....

    You were given Life Membership even before joining. What a difference, n'est-ce pas?

    Thank you for your contribution!

    After looking at the methods of securing the helmet cords, I find it anachronistically "cute" that the Japanese adopted the kabuto-method of securing a samurai helmet, vice the European strap-and-buckle.

    You mentioned the helmet worn loose, over tenugui. Wasn't the field-cap worn beneath the helmet? I was working with the JGSDF on Sakusen Yama-Sakura [command post exercise] in Sapporo and was allowed to go into their Post Exchange/NAAFI. I saw what looked like a physical training cap being sold, but it had a much shorter brim, not unlike an English public school caps [but all white cotton].

    I asked about this strange "combat cap;" the captain I was with said it was to be worn beneath the helmet, with the brim to the reverse. That was in 1993.


  10. #40


    Quote by ghp95134 View Post
    You mentioned the helmet worn loose, over tenugui. Wasn't the field-cap worn beneath the helmet?
    You can read all about that in the field cap thread I just uploaded

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