TOKYO 10, 12, 16 October 1945
Interrogation of: Captain TAMURA, Kyuzo, IJN. War time duties were devoted to Mine construction and mine sweeping.
Commander SUGITA, Binfo, IJN. Mining officer on staff of First Escort Fleet.
Interrogated by: Comdr. T. H. Moorer, USN.
Allied Officers Present: Captain T. J. Hedding, USN; Comdr J. H. Hayward, USN; Lieut. Comdr. J. A. Field, jr., USNR.
The Japanese first discovered mines in home waters in 1942. These were presumably laid by submarine. A few ships were sunk and normal sweeping operations were conducted.
Additional mines were discovered in the South Pacific but losses sustained, though substantial, did not seriously affect the line of supply. A complete record of such losses is not available at this time.
As the B-29 mining campaign progressed, the mines changed from a nuisance to a major problem. Subsequent to 1 April 1945, the largest shipping losses were caused by mines lain in Japanese waters. The Japanese were not prepared for such air attacks, and although the defense against mining was given top priority over all defense matters, countermeasures, particularly against the pressure type mine, were neither effective nor available in sufficient quantity. Finally the mines were present in such quantity and supplies were so urgently required that the Japanese were forced to sail their vessels through dangerous waters, regardless of loss.
Shipping control, defense measures, and sweeping techniques are also discussed in this interrogation. Certain technical information was furnished under separate cover.
Q. When did the Japanese actually suspect mine laying from submarines?
A. The first ones were discovered at CHOSHI and shortly after that at the entrance of OSAKA BAY.
Q. Did you detect mines in THAILAND or INDO-CHINA in October and November 1942?
A. Mines were discovered off the coast of JAPAN in January of 1943, at end of February or the beginning of March 1943. From the beginning to the end of the war the only submarine mines we knew about were the ones at CHOSHI and OSAKA.
Q. What countermeasures did you take against these mines?
A. At OSAKA, one of the mines rose to the surface, of course we simply removed it. One countermeasure in any event was ordinary minesweeping operations. The mines recovered in CHOSHI and OSAKA were in quantity of about 10 or 15.
Q. Were any ships sunk or damaged by these mines?
A. At CHOSHI, one 2-3,000 ton cargo ship; at OSAKA, about two 1,000 ton cargo ships were sunk as well as one 3,000 ton cargo ship.
Q. Was merchant ship routing changed as a result of this mine laying?
A. Yes, we simply changed the route by changing the channel; also went further off-shore and avoided points close to land.
Q. Did the Japanese encounter any mines in the SOLOMON's Campaign?
A. As far as we were concerned the definite information about moored mines was only in these two areas mentioned. We agreed that submarines were laying floating mines, but definite place of moored mines laid by submarines was unknown to us.
Q. Were any provisions made for minesweeping gear for the SOLOMON's Campaign?
A. There were no minesweeping operations in the SOLOMONS Area.
Q. Is there a list of the losses which you incurred from mines alone, (merchant ships and naval vessels)?
A. I can get the information. Our statistics are not very good because we were not positively informed as to whether or not the ships were sunk by mines, torpedoes, storms or other reasons. I have the list for seas around JAPAN and I have the total figures. But the big problem is that all the records were burned and I must go around asking for information; the figures will not be complete.
Q. At what time in the war did the mines change from a nuisance to a problem?
A. About 1 April 1945. The reason this chart was made was that, at the point the chart starts, losses from mines started to increase, (terrifically). The losses from submarines decreased.
Q. Before April 1945, did you anticipate this problem and make any preparations in the way of countermeasures?
A. Yes, but on a small scale. We found a lot of magnetic bars at SINGAPORE, we brought them back and manufactured sweeping gear copied from the English type.
Q. Did the use of these various ships (the disposing ships), the vessels to tow the sweeps and the men to man them, seriously interfere with merchant shipping?
A. The whole program was not conducted as efficiently as we would have liked. First of all we used as disposing vessels those in poor state of repair; we realized we would have to have a certain program with a certain number of vessels and personnel for security of safety for other shipping, so we did the best we could and used as many vessels as possible; but it wasnít nearly as successful as we hoped.
Q. Were you prepared in any way for our speeded up B-29 offensive mining operations in April?
A. We were not prepared. The only way we realized B-29s were dropping mines by parachute, had no advance notice, was by visual detection. We knew you would probably do it, expected to make some preparation, but we were not satisfied.
Q. I would like to know if this intensive mine program affected the morale of the crews of the merchant ships
A. The crews of Japanese merchant ships and Naval vessels were very worried and frightened by this mining, but they were all under orders and had to work through it.
Q. What effect did this have on the routing of ships, particularly after SHIMONOSEKI STRAIT was mined so heavily?
A. The materials were brought by railroad to points in MANCHURIA and then shipped to INLAND SEA ports.
Q. When did you actually close the SHIMONOSEKI STRAITS?
A. I admit that it was closed.
Q. Was the shipping situation so critical that it was necessary to send ships through the minefields regardless of the fact that the minefields were not properly swept?
A. We forced shipping through regardless of the knowledge that it was dangerous. If we suspected mines were in certain areas, we stopped shipping for one day, pending sweeping operations; but then started in again, realizing full well that ships would be lost.
Q. Will you make an estimate as to what loss the Japanese were willing to accept? For instance, if ten ships passed through the minefields, were you willing to accept the loss of one to get nine through?
A. Around June and July this year conditions were so bad that, regardless of the losses, we pushed the ships through. We never worked out a plan of percentage, I think a certain percentage of losses are expected. We place a certain area under a Commanding Officer with the responsibility of seeing that the area is clear. Then if he says it is clear, we send the ships through; if he says not, we send them somewhere else. We leave it up to the Area Commander or Port Director to route the ships. The Commanders weren't relieved of their commands if too many ships were lost in their area. We realized big losses would result and we blamed no one. In the beginning, we had half regular Navy and half reserves; the losses were terrific so we replaced them (the reserves) with regulars. But even the regulars had difficulty and there were many changes in Commanding Officers. The situation was very bad and we used the most competent personnel available.
Q. After you swept and marked the channel did you have any difficulty keeping ships in the channels? Were there many ships lost who attempted to take short cuts and who didn't follow the channel?
A. The obedience to orders in regards to channels was very good; but even so, mines cropped up in supposedly swept channels and there were losses.
Q. What was the width of the swept channels?
A. The widest channel was 500 meters. Our plans were to sweep channels from 600-800 meters, but due to shortage of sweeps the best average width of a channel we were able to produce was 200 meters.
Q. What was the procedure used in the passage of a convoy through a channel?
A. We used a lead ship and followed in column.
Q. How was the routing of shipping controlled? In other words, how was the presence of these various minefields made known to ships and on whose authority were they routed to the different ports?
A. Each naval District or Area Commander was in complete charge of convoy and routing, and had control of all shipping.
Q. Do you have a publication similar to this which traces development of your various sweeps and which shows how you made improvements as the types of mines were changed?
A. (Referred to booklets).
The magnetic pressure mine was the most difficult to sweep. This list is put out by the Navy Ministry and is a compilation by the scientists all over Japan who were put to work on developing countermeasures against mines, particularly the magnetic pressure mine.
Q. What system did you use in plotting mines dropped by B-29s and how successful were you in actually determining where these mines were in order to know where to sweep?
A. In the KYUSHU area we had a lot of radar as well as sweeps and survey crews; in the INLAND SEA Coast we had some people watching but these were not very effective methods of plotting.
Q. Was it very often that mines fell on the beach and if so do you have a list of the mines which were recovered from the ground?
A. This is the list of these found (Referred to list). This is a chart for March, April, May and June showing the different types of mines which were recovered, swept up, etc. If we didn't get the mines by the third time, we quit sweeping; only three tries to sweep. During May, June and July period the total number was 636 mines (328-209-99 added), this is the total number of all mines recovered on land in each month. All types were recovered on land.
Q. How many mines did you estimate were laid by B-29s in Japanese Waters?
A. March 450; April 117; May 414; June 1509; July 1200. Total mines estimated by Japanese to have been dropped on Japan home waters -- 3690.
Q. What information did you obtain from the Germans?
A. This type mine (refer charts) was brought by submarine from GERMANY in summer of 1942. We thought it was very funny because it was the same type as a captured American mine (Shortland Area). The Navy has a Department of Research on countermeasures against mines at Tokyo Imperial University. In my opinion the main reason for the war's ending unsuccessfully for JAPAN was the lack of cooperation between the scientists and the military. They (the scientists) got no cooperation. I feel that if they had been placed in the same level as a soldier in a civilian uniform they would have been much better; I think they didn't care or didn't try. The Navy made no attempt to put pressure on them. The following professors were engaged in mine countermeasure work:
Professors Shimizu, Kaya, Tsuboi, Hagiwara, Nigata, all at Tokyo Imperial University.
These men cooperated to a limited extent, but no real effort was made on their part.
Q. Did you ever attempt any minesweeping with airplanes?
A. We tried but were unsuccessful and stopped. We attempted to sweep the magnetic mine fields (Moored mines). The other mines were too small to find by plane.
Q. Can anyone tell us what ships were lost as a result of mines in the SOLOMONS?
A. 1942, 2 or 3 DD's, large type. I can give you some approximate figures but we wouldn't know what sunk these ships -- carriers, submarines, torpedo, or what. I only know approximate figures, the man who would know is dead.
Q. In your opinion did the mining affect the Naval strategy in any way?
A. In my opinion and according to what I have heard the only affect your mining operations had in the SOLOMONS area was to force our shipping to exercise a greater degrees of caution. It did not necessitate an overall change in strategy.
Q. Does this apply to the BALIKPAPAN, DUTCH EAST INDIES, and SINGAPORE Area?
A. Plans were not changed in the CELEBES, DUTCH EAST INDIES, SOERBAJA Areas, although losses were high, (highest in April 1945).
Q. Were all these operations furnished with very latest minesweeping equipment (Captain shows sketch of sweeping operations). Do you know what ships were sunk at PALAU by mines laid by aircraft?
A. Two or three merchant ships were sunk there by mines.
Q. Do you know how many mines were recovered or swept at PALAU?
A. I think about 15 or 16 were swept, the mooring type were at PALAU (the Mark 10).
Q. How long was the anchorage actually closed as a result of mining?
A. For four or five days.
Q. Did you continue to use PALAU as a fleet anchorage after it was mined?
A. Sweeping was very effective at PALAU against the moored type. We weren't able to enter the anchorage, but used the narrow channel as an anchorage; but were unable to get into the regular anchorage after the mining operation.
(Captain Hedding then drew plan of PALAU HARBOR and TAMURA indicated the channel which was closed -- North Channel).
Statement in regard to list of sinkings: All vessels that were sunk are on this list. (Given to Comdr. Moorer). Captain TAMURA tried to determine what ships were sunk by mines, alone, but information at the Navy Ministry is not complete enough to clearly determine the exact cause of the sinkings of a given vessel. (Refer to list turned over to Comdr. Moorer). All sinkings are listed by areas, but it is impossible to determine exactly whether vessel sunk by mines or submarines.
Q. Are the merchant vessels on this list 500 tons or larger?
A. All are over 500 tons, nothing smaller than 500 tons was navigable over such large areas.
Q. Were the SHIMONOSEKI STRAITS actually closed for any period of time; if so for how long?
A. They were closed from March 1945 up to the end of the war, during each month approximately 15 days represented complete closure due to the necessity for sweeping operations. In spite of supposedly safe periods, the danger of navigation was still existent which explains the high loss.
Q. Explain again the exact manner in which the shipping was controlled?
A. The officers of the MAIZURU Naval Base controlled shipping in the area from NIIGATA to HAGI. In the beginning of the war the Commander of KURE Naval Base controlled all shipping in the INLAND SEA, but due to severe losses in the SHIMONOSEKI STRAITS Area a separate command was set up called the 7th Fleet to oversee routing in this specific area. OSAKA Naval Base Chief controlled the KYUSHU Area and the CHINKAI Naval Base controlled the KOREAN Area. The YOKOSUKA Naval Base controlled the entire TOKYO Area. The OMINATO Naval Base controlled the HOKKAIDO Area, but the mine problem was never important in this particular area. A special command was set up under a full admiral to oversee routing over the whole EMPIRE with headquarters at TOKYO called the "General Headquarters Surface Escort Units."
Q. What is the name of the admiral and when was this command set up?
A. This command was set up in November 1943; the first admiral in charge of that was OYOBIKAWA, former Navy Minister. Approximately June 1944 he was succeeded by Admiral NOMURA, former Naval Attache to Germany.
Q. After 1942, representatives from all departments in the Japanese Navy such as gunnery, electronics, mines, etc., went to GERMANY to obtain all the information they could on what the Germans knew about your mines as well as the English mines. Those reports were brought back but the reports themselves were burned. However, I (Captain TAMURA) remember quite well the details on mines, (refers here to booklet) all of which are in a booklet awaiting translation.
Q. Did you learn anything subsequent to that time? Was there continuous liaison up to the end of the war?
A. There were occasional small bits of information from the German Attache here but nothing after the receipt of this booklet. The German Attache was not a specialist, and merely acted as a go between. For that reason when you used magnetic pressure mines, we were caught flat-footed. We immediately began to experiment with countermeasures. We had no advance notice from GERMANY.
Q. Do you think you would eventually have been able to solve the problem presented by the pressure mine? What success did you have up to the end of the war?
A. When we first discovered the mine in SHIMONOSEKI, after great difficulty, we were even able to determine it was a pressure mine. The success we had with solving the problem was very small and all details are in the chart I gave you. I think there are a great many still sunk and which we were not able to recover.
Q. Did the Japanese have sweeping equipment at all places indicated on this chart?
A. At the beginning of the war we had equipment only in areas around manor Naval bases and some equipment in secondary Naval bases; but as mines were discovered, equipment was transferred from Naval bases to cope with the mines.
Q. Did you have enough for all bases?
A. It was not sufficient. I think that the lack of equipment was due tot he fact that the Japanese in charge were little prepared for mines; we didn't commence preparations until after the mining began. In general this showed that the Japanese People were very quick to make preparations for offensive campaigns but nor for defensive campaigns. (Off the record opinion of Captain TAMURA.)
Q. In general, do you think that the mining effort we put forth in areas other than the homeland created a problem or changed any military plans?
A. In general, the prevalent opinion was that your mining measures as such would not appreciably alter our operation plans; but in explanation of that, the main reason for not thinking too well of it was that we didn't know whether or not a ship was sunk by a submarine or any other weapon. We possibly didn't give mines enough credit. To us the big danger was submarines. It was simply because we had sufficient information to chart the effectiveness of your mine warfare. In other words, the submarines were, in my opinion, given too much credit and not enough credit to mine warfare. I would give more importance to your mine warfare than my superiors, who didn't make a particular distinction as to whether or not a ship was sunk by submarine or mine.
Q. Why isn't this information available; is it because the high command in the forward areas didn't furnish the information to TOKYO or because it wasn't furnished by the masters of individual vessels?
A. The captain of a ship simply assumes that his ship was sunk by a submarine, it does not occur to him that it may have been a mine. They knew you had an electrically propelled torpedo which leaves no wake, and even if they didn't see a periscope they still assumed it was sunk by a submarine and didn't specify that it was a mine. Unless for some reason they happened to see the ship hit a mine, they assumed it was a submarine. That is why we don't have accurate figures on mine sinkings.
Q. Tell me a little more about the methods you used to discover where the mines were dropped?
A. The B-29s were picked up by radar and position communicated to coast watchers. Coast watchers picked up the B-29s as soon as they came within vision. At night they used searchlights and simply watched the mines dropped by parachute. They then reported the approximate position to the Naval Base who then dispatched minesweepers.
Q. Were you able to follow the mines down to the water by radar?
A. It's not that good, but we were working on the idea.
Q. Did you consider the B-29 mine attacks sufficiently effective to warrant redeployment of fighters and anti-aircraft even if it decreased the defense of the cities against the fire bomb?
A. We increased the aircraft units and searchlight units attached to certain areas such as NIIGATA and SHIMONOSEKI at the expense of the cities. There was still a shortage of equipment even with the increasing of aircraft units at those stated points, but as the war in the South Pacific went against the Japanese, we were able to send more anti-aircraft units to the protection of the homeland. However, the Japanese felt that the use of aircraft units as protection against dropping of mines by B-29s was more important than the actual protection of the cities, because the life lines from the continent which furnished food and supplies were of first priority. The reason why so many mines exploded by natural or unknown reasons was being investigated by several men. However, it is my opinion that most of the mines so exploded were acoustic mines and that they were sensitive enough to have been set off by natural causes such as fishes, waves and smaller vessels. I think the quantity given on this graph is grossly exaggerated because the same mine may be seen by 4 or 5 different watchers; each one is given credit for seeing a mine.
Q. Verify these numbers on this chart. It is amazing that they were only able to sweep 328.
A. I admit it is a very small quantity and feel the reason for that was inferiority of equipment and lack of ships, personnel, and sweeping equipment.
Q. Here I have some charts. Will you indicate to the best of your knowledge the shipping trend prior to and during the B-29 mining raids? Tell me if this is substantially accurate. Who can verify these charts?
A. In my opinion the charts in regard to effects of B-29 mining operations on convoy routes were substantially correct, but Admiral NOMURA's Chief of Staff will give you accurate information.
Q. Did you feel that the mines would damage the MOJI tunnel?
A. We were very concerned about the possibility of damage to the MOJI tunnel, but it escaped damage.
Q. I would like to give you a list of the areas where we put down mines and I would like to have you use that list and find out for me (1) whether or not you knew the mines were there and (2) what damage the mines did.
Captain TAMURA brought a list (as per request) of vessels sunk by mines, submarines, and aircraft in the PACIFIC OCEAN Area. He was accompanies by Commander SUGITA, Binzo, formerly a member of the Staff of the Headquarters combined Surface Escort Fleet.
Captain TAMURA delivered the information and documents previously requested as follows:
- List of personnel and equipment engaged in mine countermeasures, including those engaged in technical studies. 349 vessels and 20,000 men were engaged in minesweeping.
- Names of additional officers who can give information concerning mine countermeasures.
- A list of ships sunk in the various mine fields prior to 1945. (This list is an estimate but is a compilation of all available information).
Captain TAMURA corrected a statement made in previous interrogation. "The Combined Surface Escort Command was set up in the fall of 1943 instead of spring as previously stated."
Q. In the list of minefields which I previously gave you, did you find places in which you never discovered mines?
A. That is quite true; however, I was able to get the information on the list from people who are in the EMPIRE at the moment, so information as to other areas is very doubtful because the people who know are not available. Commander SUGITA, who was in the 8th Fleet (RABAUL), states that ships were sunk in the KOLOMBANGARA Area. Three ships were sunk by mines, other ships were assumed to be sunk by submarines.
Q. Was mine countermeasure research accelerated during the war?
A. At the beginning of the war, studies on mine countermeasures were relatively small, but it was accelerated greatly at the inception of B-29 mine laying campaign. Personnel and equipment were increased about 100 percent at that time.
Q. Up until April 1945, approximately how many scientists were engaged in mine research?
A. Up until April 1945 my department contained only 13 technicians and 50 general employees, but this was increased to 40 and 95 respectively in April 1945.
Q. When a new type of mine was discovered at outlying base was special assistance requested from your department in TOKYO?
A. In such cases the Area Commander would attempt to sweep the mines with what facilities he had. However, if any difficulty was encountered, they requested assistance from the Mine Sweeping Department of the Navy Office; and they also had access to manufacturing facilities at SOERABAJA, which maintained a maintenance shop and warehouse for mine sweeping equipment.
Q. During the closing months of the war when so much effort was expended on mine sweeping in Japanese waters, did the use of additional technicians seriously interfere with other research and development?
A. The mine countermeasure research was given first priority. We were commanded to provide results as quickly as possible; therefore, in general, it is my opinion that research on other (electronic) devices was interfered with to a certain extent.
Q. Do you feel that military campaigns outside the EMPIRE were affected by mining campaigns?
A. Planning was outside of my province, but I believe that JAPAN'S operation plans outside EMPIRE waters were not interfered in any way by ordinary mine-laying, but only by aircraft mine-laying. I wish to specify mines by airplanes because that is the only type of mine-laying about which we have definite information.
Q. Can you give me a list of ships sunk in Japanese waters, listed by mine fields?
A. All the records were destroyed by fire. I am still trying to get this information.
Q. Will you make the general statement that ships were sunk in every mine field around JAPAN?
A. Yes, at all places with mine fields (as shown on chart) ships were sunk.
Q. Did the mines interfere with the activities of the Japanese Fleet in the OKINAWA Operation?
A. Yes, there was some interference in the operation.
Q. Did the fleet ever use SHIMONOSEKI after the campaign got underway?
A. They still used it even after mines were there.
Q. Do you know how many minesweepers were sunk?
A. Twenty were damaged and practically none were sunk because setting off of the mines usually occurred after the sweepers passed over the mine. I estimate that about three of four sweepers were sunk.
INTERROGATION of Commander SUGITA, Binzo,
(Mining Officer, Staff Combined Escort Fleet)
Q. When was the Combined Escort Fleet organized?
A. It was organized in November 15, 1943 and Admiral OIKAWA was in command until Admiral NOMURA relieved Admiral OIKAWA in July 1944.
Q. What forces were assigned to the Escort Fleet?
A. About 100 -- 600 ton escort vessels, about 15 old destroyers, about 15 sub-chasers, 2 training ships, four 10,000 ton converted aircraft carriers. Each auxiliary carrier had about 12 planes (land base fighters, Type 97).
The Combined Escort Fleet, with headquarters at TOKYO, was subdivided into Naval Bases, and the First Escort Fleet, with headquarters at TAKAO. The Naval Bases included all major bases controlled by the Japanese, each of which was supplied with escort aircraft. The First Escort Fleet was composed of surface vessels and the air group which included 4 CVE's and land-based squadrons. The land-based squadrons operated at various bases along the convoy routes in the Pacific Area.
Q. Who was next in line? Did the Commander of the Combined Escort Fleet report to Admiral TOYODA, or to the Navy Ministry?
A. From November 1943 until April 1945, the Combined Escort Fleet was an independent command operating directly under the Imperial General Headquarters. Subsequent to April 1945, it was under the command of the Commander in Chief (Admiral TOYODA).
Q. How were the four converted aircraft carriers employed in convoy escort work?
A. The four converted carriers of about 10,000 tons each, carried 12 Type planes. The aircraft carriers were used to escort convoys which were larger than 20 ships. These carriers stayed with the convoy during the entire voyage to and from JAPAN. In the cases where the convoy was too small to warrant the use of carriers, air cover was furnished by approximately 175 aircraft stationed at strategic points along the route.
Q. Explain how a convoy was assembled and how it was controlled between JAPAN and outlying bases?
A. At the beginning of war, the command of the Naval District, where the convoy assembled, laid out the course and controlled the convoy until it reached the next Naval District Command on route to the destination, where they were given another set of sailing instructions. After the Grand Escort Fleet was established the Command Headquarters laid out the entire route with all sailing instructions from start to finish. When a convoy passed through the next succeeding Naval District they received all the assistance that they required but no further instructions. Air escort was furnished by the Commander of the Escort Fleet.
Q. How were merchant ships kept informed of the location of mine fields?
A. TOKYO Headquarters despatched a signal to the captain of the ship informing him of mine areas and sweeping operations. In areas outside of the home waters, Naval District Commanders informed TOKYO Headquarters and all ships of all known mines.
Q. Were MANILA and SINGAPORE ever closed by mines?
A. No, MANILA never was closed, but SINGAPORE was closed for a week.
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