Interrogation of: Commander TADENUMA, Saburo, teacher at Yokosuka Mine School from 1938 to May 1945; Kure Mine Squadron Staff Officer (81 Sohai Sentai) from May until the end of the war where he was responsible for sweeping of INLAND SEA.

Interrogated by: Comdr. T. H. Moorer, USN.


Commander TADENUMA presented a complete list of all vessels sunk and damaged in the central and western part of the INLAND SEA, the SHIMONOSEKI Straits and the SHIMONO District during the period from 27 March 1945 to August 1945. This indicated a total of 125 vessels seriously damaged and 123 vessels or 200,000 tons sunk.

Although no capital ship was damaged by a mine in the INLAND SEA, the mines seriously interfered with their movements and made it impossible to move units of the fleet without considerable difficulty. The effort to keep an escape channel open for use by the fleet led to an extravagant use of minesweepers which were sorely needed elsewhere to clear channels for merchantmen. Minesweepers were stationed along the channel to be used by the fleet as watchers and made every effort. to sweep the mine immediately after it was laid. Nevertheless, there were many cases when the fleet was held up and rendezvous delayed. In April 1945 when the Yamato and escorting vessels sortied from the INLAND SEA to move on OKINAWA, it was necessary to use all sweeping equipment available and sweep a channel of minimum width. There was no delay in this case but the fact that the Yamato was not mined was considered mostly luck. Large warships did not attempt to use SHIMONOSEKI Straits after 27 March 1945 and were forced to use BUNGO Channel. Many destroyers, submarines, and escort vessels were damaged by mines in the INLAND SEA and SHIMONOSEKI Area. In passing, Comdr. TADENUMA stated that an entire division of 4 destroyers were sunk by mines in SHORTLAND Harbor during operations in that area.

Complete information is not available as to the effectiveness of Japanese degaussing equipment. The general policy was to use the British type of equipment on large vessels. When available in 1945 the American type was installed on submarines and destroyers. Degaussing equipment was never available in sufficient quantities. It is interesting to note that mine countermeasure personnel and material became so acute that it was necessary to delegate the responsibility for sweeping the BUNGO Channel to a Special Attack Torpedo Unit which was originally organized for suicide work in the RYUKYUS.

After a discussion of mining in general Comdr. TOENUMA submitted his views in writing. They are considered noteworthy and are quoted below.

I. What We Have Learned From American Mine Attack With Our Views Upon It.

A. Views from Strategic Standpoint.
  1. From the standpoint of the blockade of our bases of operations, the isolation of chief resources supplying areas, the interception of supply routes and the blockade of important points on lines of communication etc., the mine attacks were quite effective especially in the following areas affecting our operations very much both materially and spiritually: BALIKPAPAN, SINGAPORE, SOERABAJA, PARAO, SHORTLAND, TAKAO, YANGTSE River, Southern KOREA, SETONAIKA (particularly KAN-MON area, HIROSHIMA-WAN, OSAKA-WAN), SASEBO.
  2. In the following areas the attacks were not thorough-going. TOKYO-WAN, NIIGATA Port, TSURUGA Port, HAMADA Port, SENZAKI WAN, YUTANI-WAN, HAKATA-WAN, KHRUN Port, SINGAPORE.
  3. In the following areas, if they had made intensive mine attacks, they would have been very effective OTOMARI Port, WAKKANAI Port, HAKODATE Port, MURORAN Port, MUTSU-WAN, KARATSU Port, RASHIN Port, SEISHIN Port, DAIREN Port, PORT ARTHUR, TSINGTAO Port, AMOI, HONGKONG, SAN-A (KAINANTO).
  4. Their influence upon the morale and general opinion of our people: Owing to the complete war-time control of communication and the loyalty of our men and officers, they had little influence upon the morale and general opinion of our people. From this standpoint we think mine attack will be very effective if made actively upon democratic nations.


  1. The mines were not effective enough to decide the war, but it cannot be denied that they were one of the main causes of our defeat.

B. Views from Tactical Standpoint.

  1. Not only bombing attacks of B-29's, but also their mine attacks were quite threatening and effective. They have no rivals in their carrying capacity and accuracy of their attacks with mines. Surely B-29's as a minelaying weapon were quite a hit in this war.
  2. It was quite effective that they used various kinds of mines, by which frustrating our mine-sweeping operations.
  3. Sometimes they dropped mines in adjacent seas while they attracted our attention to their bombing raid which they made at the same time. For instance we did not notice their mine-laying operations which they carried on while bombing TOKUYUMA Area. In KAN-MON Area, there were many such instances.
  4. Concerning mine-laying in the intended area: It would be most effective to cover the whole area with a great number of planes at the beginning of the attack and then to fill up with a few planes.
  5. Upon important points, discontinuous attacks would be more advantageous than continuous ones.
  6. Relation of the time of attack and weather conditions: When visibility is bad, e.g. in the night or when it is foggy or it snows, it is advisable to make an attack with a few planes; while when visibility is good, e.g. in the daytime or in the moonlight night, it is advisable to use a great number of planes.
  7. No matter whether the attack is strategical or tactical, it should be completely arranged before hand not to drop mines on land. In connection with this matter, it will be advantageous to improve mines so that they may explode the instant they reach the land or after some definite time.
  8. The mine attacks should be thorough-going and lasting.

C. Views from Technical Standpoint.

  1. The ground mines are limited in their danger sphere. It is presumed that the danger radius of the present U. S. mines is less than about 40 meters. Outside this circle the danger has never been fatal.
  2. The device to make the mine powerless after a limited time seems to be excellent for the purpose of advancing operations, but it is to be regretted that not all mines laid in our adjacent seas had such device.
  3. Offensive mines will be most effective and significant when new mines are used one after another than the same mines used in a great number.
  4. It should be given a consideration that most U. S. mines had no device to prevent dismemberment.
  5. The flash which appears at the moment when the mine leaves a plane was so remarkable that we seldom failed to judge the point where it was dropped.
  6. The present U. S. mines are limited in their utility depth, which should be improved.
  7. It would be very effective to change the sensitivity and cycle of magnetic and acoustic mines.

II. Views Upon the Future of Aircraft Mines

As has been stated above, the mines do not play any decisive role in war, but they will be valuable in future, both strategically and tactically. The atomic bombs dropped on HIROSHIMA and NAGASAKI astonished the world by their tremendous destruction, but considering that the problem of their mass production is undecided yet and that there will be much discussion upon their employment all over the world, they will not lower the value of mines.


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