The infamous General Shiro Ishii's water filter

[Sewer King]

Many thanks still again Taki! As elsewhere, your generous help with this specialized matter far exceeds most anything else about it anywhere in English. I did not answer quickly because of problems in assembling the following.

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.

-- Alan

[Akira Takizawa]

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.

The early Ishii water filters were called "石井式無菌濾水器" (Type Ishii water aseptic filter) and "石井式衛生濾水器" (Type Ishii hygienic water filter). Later, they were improved and designated as "九八式衛生濾水器"(Type 98 hygienic water filter).　The five models from Ko to Bo are Type 98.

Taki

[Sewer King]

I understand then, that Type 98 would mean the improved filter series were from 1938?

Some simple things might be inferred from the photos and descriptions of the Ishii filters:

The filters might not have been hard to crank, since the handles look short. Mechanical resistance of the porcelain filter elements was not high as water was forced through them.

Initial cleaning of the filters may have been done by cranking or pumping in reverse, to backwash the elements.

Using air pressure to test the filter elements for cracks implies a separate kit in which they would have to be submerged in water, under glass or plastic so that the air bubbles could be seen. Maybe cleaning them with calcium chloride bleach and carbolic acid, as described, could be carried out in the same kit.

Taki, in the photo of the water-filter motorcycle at the time of Nomonhan:

what is the circular emblem on the back of the water tank trailer?
Is that another circular emblem above the trailer's license plate 3 057?
Would that be a formation sign next to the star on the motorcycle's license plate?
In the small inset photo, what might the posted sign say? since it looks too small to read directly.

The other water filtration vehicle with heavy camouflage cover looks like a bus. If so, I did not know buses were in any off-road field use, let alone for water purification.

In the US Naval Technical Mission report:

"riding cars" in the water purification units, likely means "motorcycles."
"water-supplying cars" would seem to be "water tank trailers."
"waterbugs" (180 liter) might be the large canvas buckets with wire frames, as we see in the various photos.

-- Alan

[Akira Takizawa]

> I understand then, that Type 98 would mean the improved filter series were from 1938?

Yes

> what is the circular emblem on the back of the water tank trailer?

It seems the mark of waterworks bureau.

> Is that another circular emblem above the trailer's license plate 3 057?

Maybe

> Would that be a formation sign next to the star on the motorcycle's license plate?

It is a number "11".

> In the small inset photo, what might the posted sign say?

It cannot be read even on original.

Taki

[Peter H]

Another pic?

Looks near the shoreline.

[Akira Takizawa]

Ishii Filter (Model Tei ) used in the field.

Taki

[Godson]

If I may interject as a 'newbie'. Water filters are something I know a little about. Ceramic filters were well known in the 19th Century and originated with Doulton's in England, as detailed here: http://www.doulton.ca/ceramicwaterfilter.html

Respectfully.

[Sewer King]

Thanks again Taki and Peter, as always.

Anyone know what these flags are?

[Sat Mar 07, 2009 4:33 pm, "Something different" thread]

Thanks to Taki’s help in other threads, I can recognize the second flag as “Water” (mizu).
Maybe the flag is flown from a water-purification unit vehicle? so troops on the march can see it from a distance.

But even without the flag, we see a soldier drinking from a dipper at one of two large canvas water buckets. These are the same type of large buckets shown in [our discussion of] the Ishii water filter. They may be the “waterbugs” of 180-liter capacity used by water-purification units, and itemized in report cited [earlier here] from the US Naval Technical Mission to Japan.

The water buckets have cloth covers to keep out insects, or more likely dust, which may be kicked up by passing pack trains and marching troops [as in this photo]. Warm weather is implied by the shirtsleeve uniforms, with all the more reason for dust if it’s the dry hot season somewhere deep in China ...

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Another pic? Looks near the shoreline.

This seems to be the truck-mounted regimental water filter Model Ko that Taki listed earlier.

The truck itself looks like the correct Type 94 for it, although I can't see why its hoods would be open during water filter operation. Unfortunately we can't see the filter itself on the canvas-top truck bed. As filtered water is run into the large canvas "waterbug" it is distributed into the smaller canvas buckets at right and the cans at left.

The soldier at far left is holding a metal container akin to a "Jerry can." The original German design (Handkoffer) and its Allied copies are well-known, but did the Japanese Army have a standardized can of its own for water or fuel?

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Ishii Filter (Model Tei ) used in the field.

I thought this squad-level model was crank-operated, but the soldier cut off at photo top left is not kneeling down to do so. He appears to have a plunger as on the individual-level Bo model, but maybe that should not apply here? Filtered water is run off into what looks like a trough, from which it is dipped into canteens through a funnel.

The long-handled dipper here looks like the same kind the soldier is drinking from at the flagged water distribution point in the above photo.

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...Water filters are something I know a little about. Ceramic filters were well known in the 19th Century and originated with Doulton's in England, as detailed here ...

Thanks Godson, probably few of us here can claim direct experience with water purification technology, so a practical viewpoint is welcome. Incidentally, there does not seem to be any claim that Ishii Shiro was the first to do ceramic water filtration itself in Japan -- only that he perfected his own design for Army-wide use.

Amplification of earlier information is also welcome. Along with General Ishii's notorious human experiments, his water filters are widely mentioned in English-language accounts and histories of his work. But they are almost never detailed or illustrated there, leading to the origin of this thread.

Large-scale field water purification is a very specialized subject in itself, one which few soldiers have any need to know (or care) about beyond their own canteens, however vital it might be to the field army as a whole.

In this forum and elsewhere are many vast and interesting discussions about ordnance, uniforms, insignia, field equipment, warplanes, and warships. But the question seldom arises about how a modern army's water is actually supplied.

This might partly be because large unit water-filters would seldom be a military collectible, and scarcely exhibited, as Taki showed us in the Japan Ground Self-Defense Force museum.

In its time too, wartime water purification for field forces was left to the specialists. Since it would hold little interest for soldiers' memoirs we might read little comment about it today.

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The Royal Doulton name is famous for table service, but I hadn't known about its water filters. It sounds comparable to America's Corning Glass Works with its long history of both kitchenware and scientific glass.

Although the link has great detail about the action and specifications of Doulton's filter elements, there is none about the actual purification machines they serve -- the equivalents of Ishii's . An Ishii ceramic element shown in Taki's photo does resemble Doulton's, but this is probably a case of similar requirements producing similar basic designs.

Standards given for the Doulton filters reach down to the highest measurements of their porosity (in microns) that screen out bacteria from the purified water. Ions from metallic silver inclusions in the filter material also help purify. Effective as Ishii's filter was, I don't know if the microscopy available to him in the 1930s allowed him to design as closely as that for such a measurable standard.

Since Doulton filters were in use from the 19th century it could be that they were known in Japan, and if so, certainly to Ishii. A scientist is usually aware of the latest things in his field, and naturally looks to build on its newest directions and principles -- and its older ones too. That's especially true in highly specialized fields with a relatively small number of researchers. But then, the obscurity of any possible or remote connection to Ishii might be difficult to look up today.

-- Alan

[Godson]

If I might comment a little further, if Ishii "invented" his filter the year returning from a trip to Europe, he probably acquired at least some of the technology there. I would expect that the large British ex-patriot community in Japan would have had Doulton or similar filters and the Japanese probably acquired them also, those who could afford them.

With sewage used as fertilizer in the rice fields (albeit after a certain maturation in vats) until well after WWII, and domestic water often drawn from wells close to dwellings and those same fields, cholera was always a problem and possibly other tropical diseases.

There were probably similar European imitators of Doulton also.

I would guess that Ishii's innovation if any, was to use a pump to force the water through the membrane(s), rather than relying on gravity as Doulton's system did. Whether that was an a new idea at the time I don't know. One wonders what the British and German armies were doing for water filtration, for example?

More might be learned of the source of these ideas if Ishii's European itinerary is known. I assume he was in Europe primarily to research biological and chemical warfare matters?

[Sewer King]

... if Ishii "invented" his filter the year returning from a trip to Europe, he probably acquired at least some of the technology there. I would expect that the large British ex-patriot community in Japan would have had Doulton or similar filters and the Japanese probably acquired them also, those who could afford them.

By this, do you mean that overseas Britons used such filters commonly enough, whether in residence or at business?

With sewage used as fertilizer in the rice fields (albeit after a certain maturation in vats) until well after WWII, and domestic water often drawn from wells close to dwellings and those same fields, cholera was always a problem and possibly other tropical diseases.

Interestingly, I have seen almost no mention to date that the Ishii filter saw any civilian application. Since they were not secret devices and would have been an aid to public health, I wonder why not?

There were probably similar European imitators of Doulton also. I would guess that Ishii's innovation if any, was to use a pump to force the water through the membrane(s), rather than relying on gravity as Doulton's system did. Whether that was an a new idea at the time I don't know. One wonders what the British and German armies were doing for water filtration, for example?

A good question for which I expect there is an answer, but not one as ready-to-hand as with questions about ordnance, warplanes, and warships. More to the point, at that time were there military-standard machines anywhere to purify water on a large scale for armies in the field? In the 1920s-30s I expect that most of the world's armies still had a World War I outlook on battlefield support, with static armies fighting in developed regions.

Gravity-feed does seem more a feature of civil water purification plant, although done there on a much larger scale than for a battalion of field soldiers. For the military, power is cheap while portability and speed are at a premium, so the innovation of a hand-driven or motorized pump would be especially attractive.

More might be learned of the source of these ideas if Ishii's European itinerary is known. I assume he was in Europe primarily to research biological and chemical warfare matters?

The late Dr. Sheldon Harris was probably the leading English-language authority on the Japanese BW program. He mentioned Ishii Shiro's travels in his best-known work on the subject, Factories of Death: Japanese Biological Warfare 1932-45 and the American Cover-Up revised edition (Routledge, 2002), page 20:

Frustrated at the lack of military receptivity to the concept of BW, Ishii began a two-year tour of inspection and study overseas in April 1928. His study tour is shrouded in mystery, hjowever, in terms of who sponsored and paid for Ishii's expenses. It is traditional in most military establishments to send their best and brightest young officers abroad to meet their opposite numbers in other countries. At the same time, they are expected to inspect military and other installations and to gather as much intelligence as opportunities may provide. In Ishii's case, there is uncertainty as to his patron. It was later claimed that "The pushy Ishii decided he would take off on his own to Europe." [His colleague and later successor at Unit 731, Kitano Masaji] wrote many years later that Ishii paid out of his own pocket for the study abroad at first, and only received official expenses later." It is doubtful, however, that Ishii would have been permitted to go off on his own for two years. The Japanese military system was highly structured and rigid in its discipline. For Ishii to receive a casual leave of absence for two years so that he could study BW overseas, in the face of supposed indifference to BW, is a little far-fetched.

In any event, Ishii traveled around the world on his inspection tour. His itinerary reads like a travel agent's fantasy. He visited Singapore, Ceylon, Egypt, Greece, Turkey, Italy, Switzerland, Germany, Austria, Hungary, Czechoslovakia, Belgium, Denmark, Holland, Sweden, Norway, Finland, Poland, the Soviet Union, Estonia, Latvia, East Prussia, Hawaii, Canada, and the United States. How much he could have learned in such an exhausting itinerary is difficult to tell. In retrospect, it would appear to be very little. Some of the countries he visited were engaged in secret BW research, others were not. In the United States, Kitano noted later, the Japanese Embassy in Washington, D.C. "had forgotten his name, but the military attache "said that he had heard that Ishii had studied bacteriological warfare at the Massachusetts Institute of Technology at Boston [Cambridge]. Kitano was mistaken. Ishii had heard that American scientists had studied BW at the Massachusetts Institute of Technology.

It could be that Ishii merely stopped at the above countries of lesser military interest to Japan or BW interest to him, such as Latvia or Hungary. If so he would have stayed longer wherever the opposite was true, such as the future Axis partners and Allied enemies.

All the reports of Ishii studying foreign BW activity or even learning about it seem unlikely on principle. Any army's actual pursuit of BW, even at the study level, is not often open to foreign visitors, let alone their military officers. As attaches and others do today, it is possible that he could have looked at civilian medical establishments and industries of related interest. However, even that would be as much a stretch as Harris calls Ishii's unusual two-year leave.

Here are other considerations:

There seems to be little mention of what Captain ishii reported from such a wide-ranging tour.

Few of those countries on Ishii's itinerary would seem to have had even a worthwhile BW desk to gather intelligence against in 1928. The most likely might have been the Soviet Union, from which Poland suspected a germ warfare attempt during the Russo-Polish War of 1920. Even so, the USSR would probably have been even less open to foreign officers than elsewhere.

And despite the relative world peace of 1928, the world fell into the Great Depression while Ishii was touring abroad. BW study would probably have been one of the lowest concerns if at all, for major armies on shrunken budgets.

Ishii's round-the-world tour, with expenses paid from whatever source, would be an envy even today. It could have been remote even for many people of means back then. For an obscure company-grade medical officer at the time it would have been still more remarkable, whatever his medical talents.

Ishii first worked on water filtration in the late 1920s, during efforts to stop an encephalitis outbreak in Kagawa Prefecture, Shikoku. I think that a supposition of Ishii looking at foreign ceramic technologies in his overseas travel is more plausible than BW study, although we have no proof. Only, if so, why would so many questions remain about those travels? It might simply be that a comparatively harmless answer would be as entangled in the various secrecy. security, and destroyed records that surround the BW subject as a whole to this day.

Taki has shown us more about Ishii's water filters than is usually available in English, but the possibility of anything new even about them adds light to BW's dark corner in military history. Despite the various books and presentations by Harris, Tsuneishi, Hal Gold, and others, there is much about Ishii and his BW program that ends up in speculative terms -- where it remains to this day.

-- Alan

[Godson]

Perhaps this has already been discussed, but it appears that the smaller of the two filters at least may operate on a centrifugal principle to force the water through the membrane. This would make sense as a piston pump or similar arrangement might produce too much pressure, forcing undesirable particles through the membrane. I believe a centrifugal system would be in effect self-regulating as the force applied would be limited by the speed at which the centrifugal parts turned, and that in turn would be limited by the speed at which the hand crank could be turned.

[Peter H]

From ebay,seller wwkochan



Feedback from Taki:

...it is Ishii's water filter Model Otsu. The photo on Ishii's water filter is rare, because it was confidential...The photo was removed from album, so there is no information about it. It is interesting that there is a stamp "inspected by military police" on the reverse side. Probably, a censor did not know what it is.

[Godson]

... if Ishii "invented" his filter the year returning from a trip to Europe, he probably acquired at least some of the technology there. I would expect that the large British ex-patriot community in Japan would have had Doulton or similar filters and the Japanese probably acquired them also, those who could afford them.

By this, do you mean that overseas Britons used such filters commonly enough, whether in residence or at business?

With sewage used as fertilizer in the rice fields (albeit after a certain maturation in vats) until well after WWII, and domestic water often drawn from wells close to dwellings and those same fields, cholera was always a problem and possibly other tropical diseases.

Interestingly, I have seen almost no mention to date that the Ishii filter saw any civilian application. Since they were not secret devices and would have been an aid to public health, I wonder why not?

There were probably similar European imitators of Doulton also. I would guess that Ishii's innovation if any, was to use a pump to force the water through the membrane(s), rather than relying on gravity as Doulton's system did. Whether that was an a new idea at the time I don't know. One wonders what the British and German armies were doing for water filtration, for example?

A good question for which I expect there is an answer, but not one as ready-to-hand as with questions about ordnance, warplanes, and warships. More to the point, at that time were there military-standard machines anywhere to purify water on a large scale for armies in the field? In the 1920s-30s I expect that most of the world's armies still had a World War I outlook on battlefield support, with static armies fighting in developed regions.
....
-- Alan

I see I didn't answer your question directly about the use of ceramic filters by Britons overseas, but yes, such filters were widely used and of course very necessary in many places, in fact probably most places in the former British Empire. I don't know when Yokohama, the main foreign settlement until 1923, got a proper municipal water system, but there were foreign nationals, missionaries for example, scattered all over Japan, and I am sure that most of the smaller towns and villages did not get proper water treatment or supply facilities until the 1950s if not later. So, the use of filters by foreigners in Japan would have been quite common probably.

As to why such filters were apparently not used for civilian water treatment, my guess would first of all cost. Japan was spending her money on arms and industrialization until after WWII. Secondly, a Darwinist attitude to the common people and life in general, and thirdly, those who could afford them no doubt did buy and use such imported filters. Just as they bought imported cars, phonographs, radios, optics etc. before WWII. The cachet attached to "foreignness" in Japan where consumer goods are concerned is nothing new.

Incidentally, I think I mispoke in my previous post about the possibility of a centrifugal operation in the "smaller filters": the photo above with the two soldiers in helmet and the smaller pump clearly shows a man's legs between which is a piston pump similar to a bicycle tire pump. If anything it would be the larger pump which would operation on such a principle, but because it is apparently used with the main body horizontal, that may be a simple piston pump as well.

[Sewer King]

... As to why such filters were apparently not used for civilian water treatment, my guess would first of all cost. Japan was spending her money on arms and industrialization until after WWII. Secondly, a Darwinist attitude to the common people and life in general, and thirdly, those who could afford them no doubt did buy and use such imported filters ...

I did not imagine that the Ishii filters could have been adapted to regular civil use on a larger scale. Even without modern-day rates of water use, the supply for a town or city seems too large for them. Although there is little in English about his filters, there indeed seems no mention that Ishii gave any thought to civil water needs at all. But it seems as if the filters could have had other small-scale users. Just as the British used water filters when overseas, might some Japanese have had some use for them when abroad? Such as in Korea, Manchuria, or China, where there were workers for Red Cross, or South Manchuria Railroad etc.

It may be more that old-and-traditional things were often kept alongside new-and-modern ones in Japan. Travelers there before and just after the war were often impressed with this. Rather than Darwinian, it might be more from a sense of place that the Imperial military would have the most or best of some technologies.

Incidentally, I think I misspoke in my previous post about the possibility of a centrifugal operation in the "smaller filters": the photo above with the two soldiers in helmet and the smaller pump clearly shows a man's legs between which is a piston pump similar to a bicycle tire pump. If anything it would be the larger pump which would operation on such a principle, but because it is apparently used with the main body horizontal, that may be a simple piston pump as well.

All of the Ishii purifiers seem to use the same ceramic filter elements. The white cylinder lying next to the Model Otsu in Taki's photo may be it.

See also the drawing Taki originally posted, with the smallest Model Bo at bottom left. Hand-driven by piston pump, it used only one filter element.

The larger motor-driven models used at least six filters, but do not look centrifugal in action. Likely those did use rotary pumps, maybe impellers?

If the Ishii filters all used multiples of the same ceramic element, maybe the filtration rates followed by the same factor? Allowing for hand-driven power compared to motor-driven.

I think it was the US Army's field water purifiers that were centrifugal, using diatomite filters. They stood vertical in operation.

-– Alan

[Sewer King]

For incidental comparison, here are two US Army field water purifiers of WW2. These portable, electric-powered units were not in use until the war, but there is no mention of who or what company developed them.

Before then, the canvas Lyster bag served for small-unit water purification. Simple but effective, it remained in US military use as late as the 1960s and the Vietnam War.

All of the following is cited from:

Coates, John Boyd Jr., Colonel, MC, editor-in-chief; Medical Department of the US Army, Historical Unit, Army Medical Services. Preventive Medicine in World War II: volume II, Environmental Hygiene. (Office of the Surgeon General, Department of the Army, Washington DC, 1955), pages 96-102

US Army field water filter, pressure-type sandbed 10gpm, WW2.jpg

Portable Water Purification Unit. This consisted of a pressure-type sand filter, having a filter area of about 15 square feet, and a pumping unit and chemical feed section (see Fig. 10-A.) In addition, two or more canvas tanks were supplied. With proper pretreatment of the water and operation of the filter at rates not in excess of 10 gallons per minute, this unit gave good results. The weight was about 700 pounds; the heaviest single piece weighed about 400 pounds. The operation of this portable unit was as follows: When the filter became dirty, it was backwashed by reversing the flow of water. Proper pretreatment of water, by removing nearly all of the suspended matter, increased the length of filter runs, decreased the frequency of washing, and permitted effective pre-chlorination.

Although it did not use a ceramic medium, this 15-gallons (60 liters) per minute unit would roughly correspond to Ishii's filter model Otsu, also in being horse-packed.

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US Army field water filter, diatomite 50gpm, WW2.jpg

Diatomaceous Earth (Diatomite) Filter. The diatomite filter consisted specifically of a shell similar to a sand filter, with several septa or supports for the filtering layer of diatomaceous earth, and with necessary valves, piping, and controls. Various types of septa were used, including fine wire and porous refractory materials. A suspension of diatomaceous earth was circulated throughout the filter to form a thin layer on the surface of the septa. This layer, which was usually one-tenth to one-sixteenth of an inch thick, representing 0.10 to 0.15 pound per square foot of surface, formed the filtering medium. In addition to the original thin layer of diatomaceous earth, more could be added at any time during the filtering process. This process was termed “slurry feed' and was advantageous with some waters in decreasing the frequency of backwashing. Diatomite filters removed amoebic cysts and produced clear and sparkling water; they would not remove all bacteria and the usual post-chlorination procedures were necessary. Pretreatment of the water was necessary and conserved diatomaceous earth (filter aid). From 1.250 to 3.000 gallons of properly pretreated water were filtered with 1 pound of filter aid. Depending on operator skill and quality of water, some of the used filter aid could be recovered.

Two sets of diatomite filters were available. The 15-gallons per minute unit was designed to serve small field units of troops. The 50-gallons per minute unit was designed to replace the [older] portable and mobile purification units … [these] filters could be combined into multiple groups of units for serving fixed installations, such as hospitals, airbases, and posts, requiring not more than 200.000 gallons per day.

The 15-gallons per minute unit consisted of a filter and feeder section, two gasoline-engine driven pumps, four 500-gallon tanks, hose, supplies for the production of 40,000 gallons of water, and accessory equipment. The effective surface area of the filter was 3.6 square feet [and total equipment weight] was 500 pounds [and] adaptable for pack carrying by man or animals.

The complete 50-gallons per minute diatomite unit consisted of a filter unit, equipment chest, chemicals (alum, soda ash, and activated carbon), filter aid, five pumping units, four 3,000 gallon tanks, and accessory equipment (See Fig. 10-B). Total filter area was about 10 square feet … Total weight, including sufficient chemicals to produce 1,200,000 gallons of water, was 5,700 pounds … [This] produced 3,000 gallons per hour [and] was well adapted to supplying water to small fixed and semi-permanent installations ...

The 50-gallons (200 liters) model would approximate Ishii's model Ko. "Porous refractory" material in it sounds similar to Ishii's porcelain filter elements.

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Was water further treated before or after it passed through the Ishii filters? Our photos to date do not show it, but it is suggested by the US Navy Technical Mission report, which lists a trunk of “physico-chemicals” for the IJA water supply troops. The American method did chlorinate water after it was field filtered.

Unfortunately, this extensive book series did not mention the Ishii filters. Neither did it mention the German Army's methods, although it broadly noted that water supply in wartime Europe was easier than in the Pacific. Some other official US Army technical histories did compare mention enemy equipment to their own, especially when their own needed improvement.

-- Alan