Addendum to "The Evolution of the Japanese Army Steel Helmet"
Article about: Addendum to "The Evolution of the Japanese Army Steel Helmet" Ever since being forced to close my thread on steel helmets, due to persistent hijackers continuously derailing the st
Addendum to "The Evolution of the Japanese Army Steel Helmet"
Addendum to "The Evolution of the Japanese Army Steel Helmet"
Ever since being forced to close my thread on steel helmets, due to persistent hijackers continuously derailing the story, additional information gained through my research had to be scattered throughout multiple threads, as once closed, I am not empowered to reopen the thread. In order to prevent eventual loss of such update information I am raising this as a companion thread. Please do not post questions here, but post a separate thread so as not to foil my attempt to keep research results under one roof for easy access to collectors.
The IJA’s Acid Test Criteria for Steel Helmet Development
Ever since army developers had to suffer the humiliation of having their first steel helmet of 1918 taken out to firing ranges to come back bullet-hole riddled, they had to work hard on defining a level of protection a soldier could reasonably expect from a steel helmet.
In the main text, I explained that various steelworks that got involved in the production of the Type 90 steel helmet first had to get a custom helmet-testing rifle supplied by the army, but I could not say at the time how success or failure was determined in this test.
That exactly was the question put to the IJA in July 1940 by the military attaché at the Embassy of Thailand.
The IJA developers replied as follows.
We use an infantry rifle modified to a smooth bore, capable of firing a lead ball round of 10.6 grams with a caliber of 12.5 mm from a distance of 2.5 or 5 meters. The ball needs to impact the helmet at a remaining velocity of 296m/s. The resulting dent in the helmet may not exceed 20mm in size for the helmet to pass this test.
Rarity of small size helmets in the collectors’ market today.
As shown in the shipment lists below, roughly 40% of helmets shipped out to field depots were in small size. Yet examples surviving today in the collectors’ market are very rarely in small size.
The answer to this riddle was found to lie in the streamlining of size availability logistics as announced in January of 1943. See here for the full story.
The mystery of helmets stamped and paint-marked in red with a㊁
The question was first raised here. Their main use as air raid helmets for noncombatants ( Army office, hospital, prison, arsenal and depot staff) is explained here.
Supply of helmet parts to the front for field repairs
For collectors that need to be on alert against postwar tinkered examples, it should be of interest to know what degree of genuine field repairs existed during the war. This can be seen by analyzing the spare parts shipment to the front.
Shown below are excerpts from long shipping lists of supplies shipped to the front in 1941 and 1942. Helmet related spare parts are highlighted in red, which include liners, pads, split pins, chin strap rings and star insignia, all ordered separately. Paint was general use and was available in gloss or matte, of which, helmets used matte during the war.
Noticeably absent from the list are chin straps pre-cut and pre-sewn, ready for attachment. This suggests that straps were supplied in bulk and cut up and sewn on as necessary to the strap rings in the listing. Such shipments also included sewing machines, but the field repair may have skipped the strap-end anti-fraying folding and sewing seen on factory-new examples.
Also, as I belatedly noticed that I did not describe in the main text how the chinstraps were put together, I thought it important to point out that it was not one long continuous strap simply threaded through rings and a suspension loop, but composed of two straps, both anchored to the helmet ring to the left side of the head. The shorter of the two straps hung straight down, while the longer section travelled around the rear of the head to pass through the suspended loop at the back and threaded further through the ring on the right side of the head before hanging down. Thus the chinstrap did not simply push the helmet down on the head, but gripped your head tightly inside the helmet.
Last edited by Nick Komiya; 02-16-2021 at 09:33 PM.
After adopting the Type 90 helmet, the navy further developed its own model, which they called the Model 3 helmet. They seem to be nicknamed “Shipboard” helmets by collectors, but documents rather suggest land use in close proximity fighting. More here.
Last edited by Nick Komiya; 02-16-2021 at 04:26 PM.
Further to post 3 of this thread, discussing the category 2 markings found on helmets issued for army noncombatant air-raid defense personnel, Bruce and Kiipu have also brought this marking up within the context of sword markings. So for the benefit of both helmet and sword collectors, I will add a more overall view on what the marking signifies.
The chart below is posted sideways to allow you to read the English translation I added. Markings shown here are not acceptance markings confirming passing the inspection for adoption, but additional markings that indicate interim status or extraordinary reasons for adopting the weapon.
In the chart,㊁ is explained as a weapon adopted as a 二號品. 號 in this case is a legal term referring to a Kanji numbered clause attached to a regulation's article. The regulation in question is the 1939 revision of the "Weapon Adoption Inspection Rules (兵器採用検査規則)" and Article 3 therein defines in 4 clauses, the types of weapons subjected to these inspections.
Clause 1: Weapons officially designated as "Type", "Provisional Type" or "Semi Official Type"
Clause 2: Weapons other than those above that require to be issued to units
Clause 3: Materials for production of a weapon
Clause 4: Automotive Fuels
As already explained, Clause 1 items are weapons that do the actual killing like pistols and swords. Clause 2 items are scabbards, holsters, slings, ammo pouches or waist belts that come as weapon accessories.
So to get an additional stamp of ㊁ means reclassification as an "Article 3, Clause 2" item of the adoption inspection regulations. Likewise, to have a gun stamped with a ㊂ means taken out of service and reduced to a classroom sample or scrap to be recycled.
There are no factory seconds in a Japanese production system, so even when marked with ㊁, there will be an official acceptance stamp below it, signifying that it fully passed product inspection. It is rather a marking signifying "Repurposed Adoption".
I can easily imagine that issue to noncombatants as means of self-defense most likely required items to be removed from Clause 1 status not to cause conflict with the noncombatant status, though that still needs documentation proof to be stated as fact.
1941 June, Chin Strap Suspension Ring Spec Changed
The 3 rings installed within the Type 90 helmet shell for holding the chin strap tape were originally chrome plated. However, in June 1941 a proposal to switch this to a Parkerized finish or Cadmium plating was adopted at the 23rd Wartime Weapons Countermeasures Conference in order to conserve chromium. Thus shiny rings indicate earlier manufacture.
Hi I apologize for the intervention, it would be useful to add to this post also the discussion on cloth liners for Type 90 helmets I remember you posted the drawing with the introduction in December 1939 and it could be a useful addition thanks
Additional Information on Steel Helmet Impact Testing
As explained in the beginning of this addendum, impact testing of helmets at the steel works required a Murata Infantry Rifle (Type 18) modified to a smooth bore 12.6 caliber to shoot the helmet with a lead ball.
This modified rifle needed to be supplied by the army and required the army to issue a special license to possess a military weapon. Thus the dates on which the various steel works applied for this license and supply of the gun provides clues to the timing of these firms entering helmet production.
To summarize the dates on the application requests shown below they are…….
1931 August 27th Kobe Steel
1931 November Nihon Tokushuko (Special Alloy Steel)
1936 January 10th Daido Steel
This testing by a lead ball projectile remained the standard method until spring of 1945, but in May 1945, a more simplified testing method was introduced by the Osaka Army Arsenal, which consisted of dropping a 20 kg steel weight on the helmet from a given height and measuring the depth of the dent created. This was similar to the drop-weight impact tests done on Gunto.
They simply took a helmet that barely passed the projectile test and dropped the 20kg weight on it to translate the threshold value of the projectile test to that of the drop test.
However, the May 1945 report explains the technical dilemma they faced in doing this and the compromise they settled on.
By 1945, Nihon Tokushuko had pulled out of helmet production and the remaining producers were Kobe, Daido and Osaka Arsenal (first time I learn of their involvement). Of these 3, Kobe and Daido produced the bulk and the arsenal’s production was quite minimal.
A problem inherent to having these 3 production sources was that the steel used for manufacturing the helmets were all different and that would have resulted in different outcomes in identical drop tests.
Kobe’s steel was of “Cr-Mn” composition (I assume Chromium-Manganese steel) and Daido’s was “Si-Mn-Cr” (Silica-Manganese-Chromium), while the arsenal used a “Cr-Mn” variant containing “Mo-V” (Molybdenum-Vanadium). This material used by the arsenal was hardly sustainable in view of wartime resource restrictions, so future production needed to anticipate use of the former two steel alloys.
Simply translating the lead bullet test threshold parameters to each type of steel yielded the following for the drop test.
Kobe Steel (“Cr-Mn” Steel)=Drop height 75cm, maximum dent depth 9.5mm
Daido Steel”(Si-Mn-Cr” Steel)=Drop height 85cm, maximum dent depth 13mm
For simplification of practice and in the interest of mass production, they drew the final line as follows.
Drop height 80cm, maximum dent depth 11mm
This May 1945 testing method required building and setting up of guillotine-like weight-dropping jigs, which would require time, so as an interim solution, they decided to test the output from Kobe Steel at the Osaka arsenal, where there already was a guillotine and have Daido continue with the projectile tests, as they were too far in Nagoya for logistical convenience.
Addendum to "The Evolution of the Japanese Army Steel Helmet"
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