Outside of Japan it is still remarkable to see any photos and diagrams at all of this equipment, even though they are commonly mentioned wherever Ishii himself is. Even more uncommon are photos of them in actual field use, and around the battle of Nomonhan besides.
This report is the only mention I have yet seen in official US records of the Ishii filter. It is also a technical description, if only a partial one. Yet it does not call the filter by name, for some reason. That seems strange because the report was compiled directly from Japanese sources.
- US Naval Technical Mission to Japan. “References from the Committee for the Technical and Scientific Survey of Japanese Activities in Medical Sources,” Intelligence Targets Japan (DNI) of 4 Sept. 1945, Fascicle M1, Addendum M-AB, Enclosure B, December 1945
From pages 107-109:
IV. Studies on water supply operations.
1.Materials for filtration tubes and burning process of porcelain filter.
Diatom earth is the main component of the filtration tubes. The quality of the diatom earth in respect to fitness for filtration tubes will be determined by the quantity of melosira contained.
We made comparative studies of the diatom earth produced in various districts of Japan and found well qualified earth in Hokkaido and Korea.
Mixture of diatom earth (70%), clay (20%), and orthoclase (5-10%), makes the most efficient filtration tubes.
Burning must be done at 1160 oC at least.
2.Examination of filtration tubes, their preservation and chemical treatment.
Inspection and measurement will be followed by an examination of the ability for filtration of water and detection of bacteria (R. prodigiosus).
Water bubble examination must be done also, by sending the air at pressure of 1kg. from inside the tube.
Explanation. The bubbles coming out of the surface will indicate the fissures of the defects in the wall of the filter.
As a result of these examinations, 45% of the products was used to be disqualified. To prevent the growth of mould on the surface of the tube, treatment by CaCl2 solution with carbolic acid was applied.Filtration waste, deposited on the surface of the tube, will be brushed off for 3 to 5 minutes after each filtration process, so as to prevent the lowering of capacity of filtration.
As the substitute for the metal part of the filtrations set, various kinds of wood have been applied in vain.
4. Instruments for conveying water. (water distribution in the field)
For transportation by trucks, a water bug (capacity 180 liter) or a wooden vessel, and for transportation by personnel a rucksack, bamboo stem and other various kinds of bottles were used.
Waterbugs and other vessels were furnished with nozzles through which the water was distributed to the soldiers.
In certain areas, to provide many soldiers with water at one time, 2 meter long bamboo stems with 10’ nozzles were applied.
From pages 156-157:
The Ishii filters did not seem to have any kind of Type or Model numbers given to them, like those of weapons or other equipment.
I am unsure what “physico-chemical use” means in the medical stores table. It suggests various other chemicals for water treatment, such as alum, charcoal, or bleach powders. Or, it may mean a trunk of pharmaceuticals.
The filters were not secret devices, they were standard IJA equipment, and should generally have been sent to many fronts and rear areas. Since all field troops must have fresh water, US technical intelligence would have had at least some interest in knowing how the Japanese Army got it. The probable Okazaki filter shown in the US War Department Handbook of Japanese Military Forces looks too small for any unit larger than a squad. The Allies would probably have seen at least some Ishii filters by later in the war, yet no available wartime report describes a captured one.
The undated attempt to substitute wooden parts for some metal ones in the filter may be slightly puzzling. Did they contain that much strategic metal like aluminum or copper? It seems that most of their mechanisms would have had to remain metal while only the framework and supports could have been tried in wood. If so, this does not sound like a great savings unless the filters were built in very large numbers. Moreover, wasn’t there only one manufacturer?
Attention to its porcelain filter elements -- Ishii’s own innovation -- is particularly interesting. Where the report states “burning” of the filter material, it should probably be “firing.” The white piece lying next to the complete filter on JGSDF museum display looks like one of them. Except for gross intake screens, I do not know what else the water passed through besides the porcelain.
It would be good standardization if all sizes of filter used the same porcelain elements, differing only in the number of those inside. Did they?
Reportedly, General Ishii’s experience here with porcelain inspired him to make his Uji-series bubonic plague bombs out of similar material. Those were probably not of the same high-quality as used in his water filters.
The range of Ishii filter models Ko through Bo matches the range in the table above. Unfortunately the report has no drawings or photos of any of them, whether referenced, printed, or attached.
I imagined that all sizes of the filter could be hand-operated, but that larger ones on vehicles were motor-driven. Some sources mention hand cranks, and that is what the Tei and Otsu models in the museum have, although mounted differently. The smallest Bo model seems to have a piston-type pump handle that acts up-and-down.
Could it be that the JGSDF museum has the only surviving Ishii filter of that kind? It would be remarkable if another one sits in an obscure corner of an Allied war museum collection, although I doubt it.
Finally, the water purification units tabled in this report have standard loads of bandages and medic bags. Those imply that their troops were also meant to serve as ordinary field medics when not actually busy with water supply.