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Appendix H

Imperial Japanese Navy ST (SEN - Taku) Special Submarine.

When apparently reliable data became available to the author, this appendix was belatedly included as part of the main article simply because it appears the Japanese had adopted the policy of the fast battery submarine at an earlier date than the Germans. There is no readily available evidence that this submarine policy of the IJN had any significant influence on post war USN submarine policy as was the case with the German WWII submarine developments.

Whether there was any influence on German WWII designers is entirely speculative but it seems likely there would have been some exchange of ideas.

SOURCES

A. The secondary source of general data for this "IMPERIAL JAPANESE NAVY SUBMARINES" 1941-45 by Mark Stille. Stille acknowledges his primary sources. Appendix I

B. Specific primary source data regarding the submarine's cells - US NAVAL MISSION TECHNICAL MISSION TO JAPAN. Investigation carried out by Mr J.L. Rupp, civilian technician attached to this mission. Appendix I

SUMMARY of the data in "IMPERIAL JAPANESE NAVY SUBMARINES 1941-45"

The IJN had experimented with high submerged speeds using a small submarine Vessel Number 71 in the years 1938- 40. Wartime losses encouraged the development of an operational class of fast submerged submarine, the SEN-Taku (high speed submarine). 24 were ordered in the 1943-44 programme. Eight were actually laid down Only three were completed I-201, I-202 and I-203.

I-203 was damaged by air raids and scuttled in Japanese waters in 1946. The other two were taken to Pearl Harbour for study. They were tested to destruction in 1946.

Click here for a brief operational history. No doubt there are archived documents about the reported USN trials.

Stille does not make any connection to the WWII development and construction of the German of the Type 21 U-Boat, but as commented earlier, one can reasonably speculate that German designers were aware of the early development work by the IJN. Stille comments on the large German influence on Japanese submarine design up until about 1928, then gradually the Germans returned home and the influence faded as the Japanese became self-reliant, but perhaps informal contacts still lingered through the 1930s up until the war.

What impact any study of the ST had in regard to post war Allied fast submarine development is not known to the author of this article/appendix, but interestingly Admiral Galantin USN (ret), in his auto-biography makes no mention of the ST submarine or any other reference to IJN influences on USN post war submarine designs, unlike the detail he gives about German Type 21 U-Boats in experimental service in the USN.

Stille tells us that the design was very modern, fitted with snorkel and carefully streamlined with the deck guns concealed.

The latest construction techniques were used, but like the Type 21 U-Boat, the ST class were not completed in time to take part in the war.

The dimensional data given indicates the ST was a little smaller than a British WWII T Class but with far more surface and submerged propulsive power. However the T Class had more torpedo tubes. The stated ST crew of 31 is remarkably small, being comparable to the 31/37 crew of the 740 ton submerged, British U Class & V Class.

The range was significantly less than most other IJN submarines.

US INVESTIGATION INTO THE SPECIAL TYPE 'D' BATTERIES USED IN HIGH SPEED I-200 SUBMARINES

This investigation was conducted by members of the US NAVAL MISSION TECHNICAL MISSION TO JAPAN 1945 and was of many such investigations into Japanese naval vessels and equipment The members of this Mission literally landed with the occupying forces and consisted of several hundred USN personnel and significantly from an historical point of view, 23 British personnel.

The particular investigation into WWII IJN submarine cells had the prime intention investigating the battery cells used in the reported fast I-200 submarines.

The report has a lengthy summary at the beginning that starts with the bold statement -

The high-underwater speed submarine's storage battery was a two cell glorified automobile type with multiple thin plates. It was deficient in electrolyte, separation and sediment space. A multitude of parallel circuits were used. It was entirely undependable and was so recognised by the Japanese

This damning statement supported by considerable detailed investigation, as a consequence also damns the effectiveness of the ST no matter what other virtues it had as a fast submerged design and emphases the overwhelming importance of the battery in fast submerged submarines.

Extracts from the investigation report and comments are listed below for readers with a technical interest in these matters.

The report preface states "The I 201,I 202 and I 203,built in 1945, are reputed to deliver 5000 horsepower submerged and to have a speed of 16.3 knots for 50 minutes.

The battery weighs 417,000 pounds and is rated at 4,176 kilowatts at the one hour rate"

The report gives the number of cells as 4,176 with two cells in each of the 2088 containers

There no is indication of how the cells were connected for the highest speeds but there were 36 separate parallel lines connected to 116 cells each, the voltage of a each of the 36 lines was 232 volts.

The full investigative detail is far too lengthy to repeat here but a comparison is made to a standard US Submarine battery cell that has similar characteristics to that of the type named as SARGO I in Appendix a. There were cell 252 large cells per USN Fleet Submarine (submerged displacement 2400 tons).

The gist of the reported weaknesses of the Japanese battery was that the life, in terms of cycles of total watt hours per pound weight,was less than 16% of the US cell coupled with considerable doubt that all the cells would able to maintain the relatively high 'end' voltage at the one hour rate.

This conclusion was based on the US cell having a minimum guaranteed 600 cycles. It should noted that the later GUPPY high discharge submarine cells, SARGO II and the GUPPY 1, Appendix A, had cycle rates of 400 and 300 respectively. However the Japanese "D" cell was still much lower at less than 80 cycles.

One would need a more knowledge about post war US cell design and overall thinking, to pursue this aspect of the investigation any further.

The US investigators considered the plate design would make the hydrogen emission high. Good quality hydrogen detectors were fitted but hydrogen levels were allowed to rise dangerously to 6%.

The report conclusion includes the statement - "To attempt to obtain large capacity from a multitude of small cells is moving in the wrong direction ".

The investigators found that there was a new cell intended for the ST submarine (Mark 1, type 33) that went some way to improving the battery by using cells with larger plates, but many observed deficiencies remained, not the least was the lowering the 'end' voltage from 1.72 volts to 1.5.

It was felt that this reduction in 'end' volts meant that little would be gained using these new cells in the fast ST submarines with heavy discharges.

The investigator remarked that Japanese battery technology was 25 to 30 years behind that of the US and there little, if anything to learn from the investigation.

A rather poor photograph seems to indicate the numerous cells were inter-connected in the vertical plane as opposed to the usual horizontal.

The US investigator made one interesting comment that perhaps can be applied in general about the batteries of high speed submerged submarines -

The use of multiple thin plats is proper design procedure for high capacity batteries, but when rates no higher than 30 minutes are contemplated, it is useless to go below a positive plate thickness of 0.080 inches, with 0.930 to be preferred. Negatives may be made thinner by a special grid design, with some saving in weight.

Footnote

John Eade -

Perhaps it would be useful to remind readers that Japanese submarine force was a well equipped, technologically advanced, well trained force and could have been used with devastating results had the ideology and upper leadership been right. In light of Japan's other methods of defending the homeland [kamikaze] it may be that the battery technologies shortfall in recharge cycles were not seen as a long term problem

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Appendix G Appendix I