TOKYO 10 OCTOBER 1945
Interrogation of: Vice Admiral MIWA, Shigeyosh, IJN; successively Director Naval Submarine Department and CinC Sixth (Submarine) Fleet.
Interrogated by: Lt. Comdr. J. A. Field, jr. USNR;
Allied Officers Present: Comdr. T. H. Moorer, USN.
Admiral MIWA discusses general aspects of the PACIFIC submarine war including Japanese tactical and technical problems and comments on the performance of U. S. submarines.
Q. In general terms I would like to know the number of operational submarines in the Japanese Fleet during the war?
A. At the beginning of this war, the strength of submarines was biggest; as the war went on, the number of submarines decreased because of the strength of constructing submarines was not adequate.
Q. About how many operational submarines did you have at the beginning of the war?
A. I cannot give you the exact number, but about 64 submarines including the oldest style which was not operational and including training submarines; about forty or forty-five submarines completely operational. That was the greatest number we had during the war.
Q. Do you include midget submarines in that figure?
A. As for the special submarines for two-men crew, I had no connection with that submarine so I do not know about those.
Q. Who was in charge of those, another department?
A. A very few staff officers of the General Staff and the War Office knew who had charge of that special submarine. As I was at sea I did not know about it.
Q. Were those special submarines ever operated as part of the Sixth Fleet during the war?
A. During the period when I was Commander of the Sixth Fleet I never used special submarines, but I used what we call a torpedo, which had a one-man crew.
Q. In what period during the war do you feel Japanese submarines were most successful?
A. Generally speaking, the effect of success of the submarine was not so good as expected before the war. In ULITHI Operation and LEYTE Operation we had good success. On those operations the Japanese submarines were, successful; but as I was only in charge a short period of time during the war, I cannot say for entire period. Although exact reports are not available from the GUADALCANAL Operation because some submarines did not return, that period is also considered to be a period of considerable success.
Q. Could you name a period or periods during the war when submarine losses were particularly serious?
A. First of all GUADALCANAL Area and LEYTE, and also the ALEUTIANS.
Q. In those periods of serious losses, did you attribute those losses to any particular causes? If so, what steps were taken to overcome that problem?
A. The reason of such serious damage was due to your skillful method of attacking our submarines, and the main reason of your skillful attack was due to the radar; so our Navy officers studied very hard on defensive methods against your radar. We studied many methods of defense such as to paint over the hull of the submarines some material such as gum. Furthermore, an attempt was made by inclining sides of conning tower to reflect the 'radar' beam downwards into water away from your radar screen. (See sketch). This attempt however was not very successful. In conclusion we found that our submarine is not successful against your radar; so I wanted to have special submarines, very speedy underwater, and I wanted to make small superstructures for surfacing at night and also I wanted some kind of special tube to supply air so they would not have to come., up to recharge their batteries. I wanted the small superstructure and these special tubes and greater speed underwater. This was not imitative: after studying the method, we compared notes with GERMANY and found them to be the same.
Q. Did you in fact make these changes in design, and about what period of the war were those changes made?
A. The time these two methods were completed was about April of this year, these two methods of special submarine.
Q. You mentioned the fear of our radar; were you particularly concerned about ship borne radar or that which was borne by our aircraft?
A. Radar of your aircraft.
Q. Did you use search receivers on your submarines?
A. Yes. On the operation of the ALEUTIANS, the Japanese Navy found out your radar was very good because our submarines maneuvering in the fog received much gunfire from your ships; so we found out you had very good radar. At the operation of the ALEUTIANS, we had not that device against radar; but after that we studied and made something like that device, but it was not successful. Towards the end our device against radar was progressing.
Q. When was radar first installed on Japanese submarines?
A. I remember that about June of last year, at about the time of SAIPAN operation, that was the first time it was installed.
Q. At the start of the war was the general plan to use submarines as auxiliaries to the fleet, or to attack our shipping, or what kind of use?
A. The fundamental nature of the mission of our submarines is as auxiliary to our fleet. After the beginning of the war, by and by our submarines got the mission of attacking your merchant shipping; but the fundamental mission is auxiliary to the fleet.
Q. What reasons brought about that change -- the assignment of that mission to attack merchant shipping? Why was it done, and at what time?
A. There were two reasons for it: the principal reason, your American fleet did not offer battle so our submarine had not targets to attack; another is that the Germans wanted it. I am not sure but I think the Germans wanted JAPAN to attack merchant shipping by our submarines.
Q. What period of the war do you mean when you speak of this change?
A. That new change is about after the MIDWAY Battle. As I said before, by the request of GERMANY our submarines attacked your transport ships in the INDIAN OCEAN or near AUSTRALIA until our loss of submarines increased in the INDIAN OCEAN; and also we wanted to gather all our submarines to attack your battleships, to defeat your advance in the PACIFIC OCEAN.
Q. What makes you believe that change was made at the request of the Germans?
A. As I was officer of submarine, I wanted to attack your fleet; but I received orders from our headquarters to attack merchant ships in the INDIAN OCEAN near AUSTRALIA; so I said headquarters has some reason for that order, and I thought it was by GERMAN request.
Q. Do you feel that was a poor thing to do, do you feel it was unwise to use submarine in that fashion?
A. We wanted to attack your fleet, and the strength of JAPAN's submarines was not big enough to attack merchant ships; we wanted to attack American Fleet.
Q. What were the dates of beginning and ending this use of Japanese submarines against merchant ships in the INDIAN OCEAN?
A. From memory, approximately began May or July 1942, and ended about July of last year 1944.
Q. We were always a little surprised you did not use submarines against our merchant ships in the Central and South PACIFIC, on ships en route to GUADALCANAL. I wonder why you never did that to any degree.
A. The scouting of your planes was very severe, and another reason was our strength was not big enough for such attack.
Q. In the early part of the war we were much impressed with the effectiveness of your submarines in search and scouting in coordination with large seaplanes and with your carrier forces. Was that a planned employment?
A. Submarines had scout planes on board and as your strength of scouting planes increased, that effectiveness grew less.
Q. I was thinking rather of cooperation between submarines and large flying boats.
A. The coordination between the flying boats and submarines was not as successful as you think.
Q. Did you find it possible to have satisfactory communication between submarines and flying boats?
A. That was not satisfactory, communications were not good.
Q. Did you ever use the submarines to scout for your carrier forces? We thought at one time your submarines reported to carriers where we were, and the carriers then launched their planes for attack; is that correct?
A. Our submarines reported the location of your fleet but not directly to the carrier. The submarines would report to headquarters and these reports would be relayed to the fleet. The carrier planes themselves made searches and did not expect cooperation from submarines. Generally speaking, the cooperation between aircraft and submarines was not satisfactory.
Q. Early in the war, for the first year of the war perhaps, your submarines made us a lot of trouble but later on we had very little trouble with them. We thought that perhaps you were using them for supply and not attack; is that correct?
A. You are right, that was the very reason. That reason was not satisfactory for the submarine officer because he wanted our submarines to be used to attack your fleet, not using them for transport.
Q. Aside from the personal wishes of the submarine officers, do you feel it was wise from the point of view of the war as a whole?
A. Aside from the feeling of the submarine officers, that is still not wise.
Q. Why, then, were they used for transports?
A. Headquarters made that decision. I do not know the reason because the Naval General Staff made the decision, and several times I reported to them that these tactics were not wise; but nothing was done.
Q. Do you feel that perhaps this was done due to the Army pressure rather than being the decision of naval officers?
A. In my personal opinion, I feel that Army request was the reason. Another reason is that our headquarters thought that the supplying for the islands is very important because many soldiers were on several islands, and they would have no food or material for fight; that is important matter.
Q. In regard to the use of submarines as transports, the transport between JAPAN and GERMANY, were many submarines employed in that route? What types of cargo or personnel did they carry?
A. Some three or four submarines were used for transport between JAPAN and GERMANY. These submarines went to GERMANY with gum and tin, brought back mainly arms, plans and samples.
Q. In the transport to the South Sea Islands I presume you took in ammunition and food; what did you bring back if anything?
A. We came back with our wounded and sick soldiers.
Q. What did you take in principally -- ammunition, food, what type?
A. Principally rice and food and clothing and arms.
Q. Wasn't any importance given to bring back specially trained people, mechanics, etc.?
A. We did not bring back special personnel.
Q. We thought at the time you were evacuating maintenance people from the Northern SOLOMONS ; is that untrue?
A. A few times one or two personnel were taken back; our aim, however, was to get sick personnel back.
Q. Do you feel that any good for the war came from this transport duty, was the use of submarines for transport profitable in any way or entirely useless?
A. It is quite bad tactics; it is senseless.
Q. With regard to the building of small submarines, the two men submarines, what was the principal purpose of that program and why, particularly toward the end of the war, did you build so many?
A. As I was not in charge of that building I cannot say. I think, however, the reason is that our Japanese Navy expected your force was going to land on our land; so to defend against landing, we built up that small special submarine, and as we had no strength to maintain the strength in big ships, this was invented.
Q. However, some of these small submarines were built before the war; what reasons were there at that time?
A. I think perhaps that the special submarine was to be used for fleet operation to attack your fleet.
Q. Do you mean in PEARL HARBOR or anywhere in general?
A. They did not think at all about PEARL HARBOR attack, but in general use for any attack.
Q. But they have short range, how could they expect to use them?
A. They wanted to use that submarine in the operation of fleet against fleet, to put submarine in front of our fleet and attack your fleet.
Q. How would the submarine get there, from a base or carried by a ship to the action?
A. They were planning to bring that special submarine on board of big ship. They had a special carrier for that submarine, it was sunk near GUADALCANAL (CHIYODA).
Q. Was there ever a thought of carrying these small submarines on YAMATO or MUSASHI?
A. The MUSASHI and YAMATO were top-secret. I did not see and do not know, but it is first time I heard of such a suggestion.
Q. The small submarines that were at PEARL HARBOR, how did they get there?
A. Those special submarines were transported by other big submarines.
Q. How many small submarines could each big submarine carry?
A. Only one submarine.
Q. Toward the end of the war you began to build very large submarines of 5,000 tons. What was the reason for beginning the construction of that very large type?
A. They were planning to build these big submarines to take fighter planes to sea, and that fighter from the submarine would attack your carrier.
Q. That seems a great deal of effort in construction and material just to get one plane to attack our carriers. Do you feel that was a wise plan?
A. I think it was not wise plan, I opposed it.
Q. Whose plan was that?
A. I think that was planned by Admiral YAMAMOTO, so nobody could oppose it.
Q. If they were planned as long ago as that, was the original purpose to attack our carriers or perhaps attack the UNITED STATES?
A. That plan may perhaps have been for attacking your cities but as war went on that plan became impossible, so they planned to attack your carriers. As Chief of Submarines Officers I opposed it completely. At first this plan was to build about seven or eight such big submarines but due to the many adverse opinions they decreased that number and planned to build about four of them.
Q. Quite apart from tactical use, what is your opinion of the submarine?
A. The submarine is not a good submarine, as a submarine, and your defensive methods prevented its use. It handled rather well and dove well, but superstructure was very big, a weak point against radar.
Q. Was this type submarine ever used in an operation?
A. It was under the training, but during the period when I was commander of submarine fleet it was never used actually in operation.
Q. As far as you know, it was never actually used during the war except in training?
A. I think they have never used it.
Q. Did they ever use Japanese submarines to attack our submarines?
A. We once used submarines that way. Last year about June our Navy found your submarine near OKINO DAITO SHIMA and we sent out two small submarines; but it was not successful.
Q. Did you ever have any reports that your submarines had found and attacked our submarines?
A. I received two such reports, one was near SINGAPORE, another was south of TRUK. The first occasion occurred in early part of the war, the second occasion I do not remember exactly but about April 1943.
Q. What results did you have from your joint operations with German submarines that came to SINGAPORE?
A. Our Japanese submarines never joined up with German submarines.
Q. But German submarines did operate from SINGAPORE, didn't they?
A. I think from PENANG. The Germans were independent, we had no communication. Our Navy helped to get fuel for the German submarines but had no connection with control of their operation.
Q. Do you know roughly how many Japanese submarines were in the Central PACIFIC at the time we attacked MARSHALLS-GILBERTS?
A. Approximately 20 Japanese submarines, one-third on station at any time.
Q. Were your forces at that time still weakened by that operation in the INDIAN OCEAN against our merchant shipping?
A. Yes, that is correct.
Q. In the planning for defense of MARSHALLS-GILBERTS and your PACIFIC Islands, was it expected your submarines would cooperate with your fleet or attack our fleet on their own? Did the submarine officers expect the fleet to join them?
A. Our submarines, themselves only, to attack your fleet; they did not expect cooperation of our fleet.
Q. In the early summer of 1944 did the same condition prevail or did they expect to cooperate with the fleet? That was before our attack on the MARIANAS.
A. I was not actually in charge of that operation but suppose there was slight difference in that operation. Our submarines expected assistance of our fleet but it was not satisfactory.
Q. We would like to talk about use of submarines in the PALAU and PHILIPPINES Operations.
A. When the PALAU Operation was begun in September of last year, we sent out four submarines to PALAU Area.
Q. What success did these submarines have, do you know?
A. We sent out three submarines to PALAU and one to HALMAHERA, and two of these sent to PALAU did not return. At PALAU, our submarines sank one cruiser or destroyer and one transport; at HALMAHERA, they reported one aircraft carrier sunk and one damaged.
Q. After these two operations at PALAU and HALMAHERA, how did you dispose your submarines for PHILIPPINE Operation?
A. We disposed approximately seven submarines in the sector between northeast and southeast of LEYTE and three off LAMON Bay.
Q. Was this all the submarines you had available?
A. That was all the submarines available. Of course we had others in home waters.
Q. When did these submarines arrive in the area off the PHILIPPINES?
A. Only three submarines of them could report here on 25th morning of October, the others were still on their way, We got report which indicated that your Task Force appeared off FORMOSA, so we sent out submarines off FORMOSA. Your Task Force retired to east and we got a report the American Task Forces was going east, so we tried to intercept with submarines; but failing in this, submarines continued onto the LEYTE Area. Three submarines could reach here by the 25th, and by the next day all ten of these submarines had arrived.
Q. Was this deployment of submarines off the PHILIPPINES part of the SHO-GO Plan?
A. Yes, that is right. It was planned in advance and was part of the SHO Operation on orders from Combined Fleet.
Q. About the 17th or 18th of October, as our fleet was moving toward LEYTE, did you have submarines in the neighborhood of PALAU?
Q. During the LEYTE Operations then, in late October, ten submarines were all you had there. Did more go in later?
A. That ten submarines was full strength of our submarines; some of them were damaged so our strength there decreased.
Q. How many were lost?
A. I remember that five submarines were lost.
Q. You said that one submarine attacked our aircraft carriers off HALMAHERA; was that the RO-41?
A. That is right, it was a small submarine.
Q. What instructions were given the submarines sent to LEYTE?
A. There was no special mission but they planned to attack your fleet because we were expecting the LEYTE Operation.
Q. Did your submarines there have knowledge of the plan of the Japanese Fleet; did they know, for example, KURITA was planning to enter the Gulf that day?
A. They knew that, these submarines knew that very well because the plan of operation was made by the Combined Fleet.
Q. And each submarine commander had a copy of the plan?
A. I think that each commander did not have a copy but had been instructed by the radio.
Q. What successes did they have off LEYTE?
A. I got report that two carriers and one battleship and one big transport and five or six small transport ships were sunk, but I am not sure of the precise count.
Q. In general, was it your policy to believe reports from the submarine commanders? How did you assess the reports?
A. We believed the report from the submarine commander. I believed completely the report from the submarine commander because I did not know how many percent to decrease the report; and I gave quite a severe order to the submarine commander to make an exact report and to report the exact damage to the American Fleet. I considered the submarine captains to be honest, and we gathered submarine reports and sent them to headquarters, and headquarters judged the report.
Q. After the LEYTE Operation what use was made of the submarines?
A. None of my submarines were in the PHILIPPINES inland waters. Several midget submarines were stationed at CEBU, but these submarines were not under my control.
Q. Who had the control of these submarines?
A. It was under the command of the Southeast Area Fleet, Admiral MIKAWA.
Q. In general, were the small midget submarines assigned to Area Fleet commanders as in this case, was that the usual practice?
A. That is correct. This special submarine is not in the category of submarine and was not under my control. These special submarines were divided in several groups such as those under Admiral MIKAWA. The one-man torpedo-submarine was, however, under my control.
Q. Who controlled the submarines which attacked our ships in ULITHI?
A. I sent out eight one-man torpedo-submarines to ULITHI to attack your fleet; they were transported by two regular submarines.
Q. In your opinion was that one-man torpedo an effective weapon?
A. I think it is a very good weapon.
Q. In general now, considering the operations throughout the war, what usually limited the length of time a submarine could stay out on patrol? Was it fuel or shortage of torpedoes?
A. That limit is due to the fuel and oil and water and health of the crew.
Q. These problems forced them to return before they had the opportunity to use up their torpedoes?
A. They were very rarely forced to return because of shortage of torpedoes.
Q. Again considering the war as a whole, what particular problems did you have in operating submarines, what problems were most serious?
A. First is your attacking force was increasing attack on our submarines, damage was increasing, construction of submarines could not keep up. These were the main difficulties. Secondly, the skillful well-trained crews were lost and the new trained crews were not satisfactory for operation, but our submarine crews never get tired of submarine operation. There was no trouble with morale, and the numbers of Japanese Navy sailors who wanted to be submarine crewman was increasing. They volunteered.
Q. Did you frequently have submarines return with damage from our attacks?
A. Very frequently.
Q. Why didn't you build more submarines? Did you build as many as possible?
A. Our Navy was obliged to build battleships, aircraft carriers; so the limited material was divided and we could not build many submarines.
Q. Which type of ship was considered more important?
A. I cannot list the order of importance of construction but our headquarters allocated the limited material for the various kind of ships.
Q. Were submarine operations ever hindered by shortage of fuel?
A. We always had plenty of fuel, so far as submarines are concerned; plenty of fuel.
Q. What particular material shortages were most critical?
Q. What is your opinion of American methods of attacking your submarines?
A. It was quite skillful.
Q. Did you have good information on our methods from submarines which had been attacked and which escaped and returned?
A. Our submarines which were attacked by your force, many of them did not get back so we did not get much report. I did get general opinions and beliefs about the method of attack.
Q. Which type of attack did they fear most, aircraft or destroyers and escort ships?
A. Of course from the aircraft.
A. Your aircraft with radar attacked at night when the submarine is floating.
Note: This statement is of interest in that only three submarines are known to have been sunk by our night air attack during the entire war, of which two were German and one Japanese, all three of which were sunk in the Atlantic Ocean. Of Pacific night air attacks on submarines, four are presently assessed as "probably sunk"
Q. Did you feel that our ships had effective sound gear for listening to your submarines and following them and attacking?
A. I got quite a few reports that our submarine was attacked by your destroyer or other ship which had device for listening to sound of engine.
Q. Did you have any knowledge of our method of hunting a submarine by coordination between our ships and planes?
A. I think that coordination between destroyer and aircraft was very skillful; we feared it very much.
Q. In general did you feel that when our destroyers and ships detected the submarine they were persistent in attack, or did you feel that they were easily discouraged and soon gave up the pursuit?
A. I heard very often that your ships were persistent around Japanese submarines.
Q. Did the Japanese get any information of value from the Germans, any useful information which came from GERMANY?
A. We got many good information concerning methods of using devices against radar.
Q. What is your own professional opinion of American submarines and tactics? Do you feel they operated well? In what particulars were they weakest?
A. American submarine crews were very well trained, skillful, and brave. It was unexpected, we did not expect such skillfulness. This is not a compliment but the truth. One instance is our Japanese carrier going home from the south area of the PACIFIC. That carrier was attacked in the night, wind speed at 20 meters, just a single submarine and the same one attacked twice again the next morning.
Q. Which carrier, do you know the name?
A. I don't remember, but the attack was about October of last year, before the LEYTE Battle, off TOKYO Bay. Another example is the sinking of the KONGO. As Commander of the Sixth Fleet, I discussed this operation by the American submarine with my officers, saying it should be an example to our own forces of a brave skillful operation. I had no knowledge of the weaknesses of your submarines.
Q. Do you feel that the success of our submarines was due principally to superior skill, or to better devices and technical study?
Q. You said you did not expect this to be the case at the start of the war, I wonder why?
A. I expected that your submarine crews would be all on the same level with Japanese crews and likewise the devices of submarines; but they were superior to the Japanese.
Q. Do you feel that the operations of our submarines had any decisive influence on the winning of the war, do you feel that some other ship was more important?
A. I think that is a very important reason, but perhaps not the most important reason.
Q. What other particularly important reasons, such as that one, do you feel influenced the course of the war?
A. I think the most important reason is your aircraft strength.
Q. What particular type of aircraft or implementation of aircraft was most important?
A. I am not expert with aircraft but of course the B-29's did great damage in the last few months. Our war was lost with the loss of SAIPAN. I feel it was a decisive battle. The loss of SAIPAN meant you could cut off our shipping and attack our homeland, and our submarine operations were completely shut out.
Q. At the beginning of the war did you expect a long war or short war?
A. I thought, this is my personal opinion, that war against America was very dangerous, we had very few chances to get away with it. Japanese military forces have many weak points, but American force has no weak point. During the period when I was a student at the Navy Staff College, I had the opinion which indicated that we should not have the war against America.
Q. Was that your opinion, or were you told that at the Staff College?
A. That was my personal opinion from the time when I was a youngster; the Japanese have many weak points, Americans none, war against America is not good.
Q. Was the Army more eager for war with America, did it have more optimistic view than the Navy, do you feel that the Army was willing to fight America?
A. We must not say such a thing, but you should understand that I know one Navy officer who has such an opinion.
Q. We understood that toward the end of the war, the Army was building submarines to operate itself. That seems somewhat peculiar. Do you know what the reasons were?
A. When the Army planned that building up his own submarine, the Navy side opposed that plan; but the Army answered they were planning on building up special submarine for supplying these islands and Army didn't want to use Navy submarine for such supplying because Navy submarine had more important mission to fight with fleet, and the Navy agreed with that plan. The Navy explained to the Army that building of submarine very difficult, and they wanted to show how to build them; but military did not want to be assisted by Navy, so military themselves built the submarines.
Q. Did they work?
A. I do not know about military submarine, but I think they were of no use.
Q. When the Navy submarines were supplying Army troops, were these operations controlled by the Army or the Navy at that time?
A. It was undecided.
Q. Who ordered them to do so, and told them where to go and what supplies to carry?
A. Concerning the operations of supply submarines, the orders issued from Navy Southeast Area Command; for the material to be located on board the submarine, that order came from Imperial Headquarters.
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