TOKYO 22 October 1945
Interrogation of: Captain TAMURA, Kyugo, IJN. War time duties were devoted to mine construction and mine sweeping.
Interrogated by: Comdr. T. H. Moorer, USN.
This interrogation is a continuation of NAV 5.
Captain TAMURA discusses the mining of Japanese waters and furnishes additional facts and opinions relative to the various phases of mine warfare.
Captain TAMURA submitted the following information which was requested at a previous interrogation:
- List of vessels sunk or damaged in minefields on West Coast of JAPAN north of SAKAI.
- A complete list of vessels sunk in SHIMONOSEKI Area.
- A complete chart showing all channels in the SHIMONOSEKI Area and location of mined vessels.
- Table showing passage control through SHIMONOSEKI Strait in July 1945. Records for April, May, June and August were burned but are stated to be similar.
- Number of passages through SHIMONOSEKI Strait during July, showing number of vessels hit by mines.
- Estimated number of B-29s laying mines in SHIMONOSEKI area by date.
- Results of minesweeping in SHIMONOSEKI Area, including number of mines swept.
- A brief description of Japanese minesweeping equipment showing area where employed.
Q. Captain TAMURA, in addition to the information furnished by you at previous interrogations, do you have further statements to make in regard to the offensive mining campaign by the U.S. Forces?
A. If you had been able to disguise the places and times of the dropping of mines by your planes our counter-measure research would have been delayed and losses would consequently have been greater. Even though we had a difficult time in working up counter-measures against mines, it would have been much more difficult if we hadn't been able to watch planes drop mines and recover them immediately. The important thing is not to let the Japanese know you were dropping mines. Another weak thing was so many dropping on land, making recovery easy. Also when you dropped mines by parachute it would have been better to drop from a lower altitude in which case you wouldn't have taken them in to land. It was very effective when you dropped mines with a new device in it. During the period after a mine with something new is used, there is a period of recovering it, taking it apart, finding a counter-measure, then constructing the machinery and educating personnel in using the equipment. There was a one or two month lag during this particular period when we didn't know what the solution is and took big losses. Then you should drop more of these mines because we do not have a counter-measure for that particular mine. One thing that caused us much trouble was the combination of two types of mines, combination of magnetic- acoustic and the magnetic-pressure mine. By the end of the war we were left with a lot of research being done but no real effective counter-measure being produced in quantity. I think that you should have tried to develop something to prevent those spontaneous explosions and sympathetic explosions. I tried to work on it but couldn't find out why so many of your mines exploded for no apparent reason. It is something worth studying. It might have helped if your mines had been dispersed more.
Q. What features of American mines were you unable to solve? What particular feature of the American mines did you know the least about?
A. No part gave us particular trouble because our engineers were able to take the mines apart, and to understand it. The pressure mine was a big puzzle to us because we couldn't figure out what set it off. The fact that it was a pressure mine caused us trouble. The magnetic mine caused us trouble but we knew it was a magnetic mine and could understand it. We could take each one apart but the
parts didn't add up to anything. We picked up the first magnetic pressure mine in May 1945 and by the end of June were able to sweep it. We were successful in completing the major portion of the research and knew the story by that time. We were able to sweep two or three at NIIGATA in August but the war ended before we had any more experience in sweeping.
Q. How did you sweep the magnetic pressure mine?
A. The mines at NIIGATA were swept in very calm water with a hydro-bar. The big disadvantage of dropping mines by plane is that the planes are easily seen and the mines are marked. A combination of submarine and airplane in placing the mines is an idea. An airplane to drop the mines far enough off shore so that the coast watchers are not advised and submarines to pick them up somehow and pull them in to shallow water in some manner. Mines well laid by submarines are more of a surprise. The submarine could very successfully lay the moored mine a lot easier because it doesn't have to be laid at such shallow depth. According to information from the Germans this was very effective.
Q. Do you think that the mine fields laid by the B-29s were effectively placed?
A. Your campaign was very well conceived.
Q. Did the mining of any of the distant ports, such as RASHIN, take you by surprise?
A. No, we weren't surprised because it was keeping with your policy of mining busy ports. During the early part of this month the storms around JAPAN caused many mines all over to explode. Not only acoustic, also pressure mines.
Q. Are you familiar with the low frequency acoustic mine?
A. Yes. We tried many different methods of countering it but were not successful.
Q. Were you able to successfully sweep the low frequency acoustic mine?
A. No. I think there is still no effective counter-measure in any country for the low frequency acoustic mine and the magnetic-pressure mine.
Q. Did you attempt to sweep pressure mines by towing a large canvas sea anchor?
A. That is one of the methods. We tried thousands of ways. The use of the bag was one of them; the closest thing to success was the hydraulic plate.
Q. What in your opinion was the best method for mining by airplane? Is it best to drop a great number of mines at intervals, or to drop a few every day?
A. In my opinion continuous mining is more effective than occasional large scale mining. Of course the large scale attacks at intervals also cause a lot of trouble, but when you continually dropped them it meant that we were using equipment 24 hours per day. They were always on the lookout. Whereas, a big load dropped at intervals, we had a respite for a few days. A continuous defense is hard to keep up. From the point of view of a long war, it is far better to continuously feed mines to a given area because we never are confident of a swept channel. With a big load in one place we know it is clean when swept.
Q. In your opinion, Captain TAMURA, do you think the UNITED STATES divided their mining and bombing effort properly? In other words do you think we should have increased our mining effort and possibly commenced mining operations sooner?
A. The result of B-29 mining was so effective against the shipping that it eventually starved the country. I think you probably could have shortened the war by beginning earlier.
Q. Do you think that the planes used in mining were more effective than an equal number of bombing planes?
A. Yes, I do.
Q. Was the SHIMONOSEKI channel ever fouled by sunken ships?
A. No, because it was too wide for that.
Note: Interrogation NAV No. 27 (USSBS No. 104) is omitted from this series as it contains limited information which amplifies and clarifies answers to questionnaire contained in NAV MEMORANDUM --6 which was submitted to the Japanese Government.
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