Interrogation of: Rear Admiral MATSUZAKI, Akira, IJN, who served as Chief of Staff, Second Southern Expeditionary Fleet, April 1943 to February 1945 and Chief of Staff OSAKA Naval Station, February 1945 to August 1945.

Interrogated by: Commander T.H. Moorer, U.S.N.


Rear Admiral MATSUZAKI discusses the effect of mining on the SOERABAJA, CELEBES, and BORNEO Areas as well as the organization and operation of mine defenses at OSAKA.


In response to questions submitted directly and by letter, Rear Admiral MATSUZAKI furnished the following information.


The Southwest Area Fleet was organized as shown below:

Southwest Area Fleet First Expeditionary Force
1st Base Force
2nd Base Force
3rd Base Force
Second Expeditionary Force
1st Base Force
2nd Base Force
3rd Base Force
Third Expeditionary Force
1st Base Force
2nd Base Force
3rd Base Force
Fourth Expeditionary Force
1st Base Force
Air Force

The Second Expeditionary Force at SOERABAJA was responsible for mine counter-measures in the BORNEO, CELEBES, and JAVA Areas. In these areas mine sweeping was a continuous process. During the first part of 1943, the magnetic mine was difficult to sweep but the problem was solved when magnetic bars were procured from SINGAPORE in September and October. By the end of 1943, mines became of serious consequence. A radar warning net was established, as well as a system of watchers. By tracking planes with radar, an effort was made to establish dropping points. Night fighters were used but proved ineffective.

Beginning in 1944 mining had a considerable effect on the exploitation of the vast resources of the NETHERLANDS EAST INDIES. Not only were ships and cargoes destroyed but convoys were delayed, and unloading areas were jammed at SOERABAJA and BALIKPAPAN pending sweeping operations. The destruction of tankers and delay in oil shipments was particularly serious.

Due to use of small wooden ships, mining had little effect on the supply to garrisons. Mining countermeasures involved the use of 1500 men and 30 ships in the CELEBES, BORNEO, and JAVA Areas. Nevertheless about 40% of all vessels over 1000 tons which sailed into the BALI KPAPAN-SOERABAJA Area, were sunk or damaged by mines. In many cases ships were salvaged only to be sunk the second time. Even before the capture of the PHILIPPINES, the traffic to the NETHERLANDS EAST INDIES was reduced to a trickle. After February 1945, no attempt was made to use large ships and only small schooners and wooden barges were operated.

Note: Quoted below is the exact report as submitted by Rear Admiral MATSUZAKI. It is considered important since it effectively illustrates how totally unprepared the Japanese were for large scale mine attacks.


Counter-Measures Against Mines Laid By American Aircraft in Osaka Area

  1. Counter-measures employed in view of the conditions of mine laying by the UNITED STATES aircraft in the KWANMON Area.

    1. Establishment of magnetic mine sweeping unit at KII Defense Garrison (YURA). Order was issued to establish magnetic mine sweeping unit on April 5, 1945. Launched immediately on preparations.

    2. Establishment of OSAKA Port Defense Garrison and KOBE Port Defense Garrison Order was issued on May 1, 1945 to establish newly the OSAKA and KOBE Port Defense Garrisons. However, the mine sweeping strength could not be mobilized until the early part of June.

    3. Preparation of mine sweeping by use of sound bombs from airplane at KOMATSUSHIMA and KUSHIMOTO Seaplane Bases.

    4. Established look-out posts for mines along seashores of OSAKA-WAN, HARIMANADA, and AWAJISHIMA in early part of April.

    5. Prepared a map as of 4 April 1945, showing the channels to be swept and so got ready for counter-measures against mine laying.

    6. The strength of each mine sweeping unit as of 4 May 1945 (U. S. planes laid mines in OSAKA-WAN for the first time).

      1. KII Defense Garrison
        Type 5 mine sweeper
        Mother boats (converted sub-chaser 3
        Side boats (fishing boat) 9
        Type 3 Model 2 mine sweeper (fishing boat) 10

      2. OSAKA Port Defense Garrison; KOBE Port Defense Garrison Strength: None

      3. KOMATSUSHIMA and KUSHIMOTO Seaplane Bases Scout seaplanes 6

  2. Mine sweeping during the early period of mine laying in OSAKA-WAN by U. S. planes.

    1. Magnetic mine sweeping unit of the KII Defense Garrison was advanced to OSAKA-WAN and engaged in mine sweeping.
      Strength: Type 5 mine sweepers 2 units
        Type 3 model 2 mine sweepers 3 units

    2. Mine sweeping with sound bombs by planes of KOMATSUSHIMA and KUSHIMOTO Seaplane Bases. The mine sweeping was done by a total of 6 planes on 4, 5 and 6 May.
          Total number of mines disposed ............................................... 15

  3. Mine sweeping and counter-measures after the above period.

    1. The mine sweeping units of the KII Defense Garrison were stationed permanently at OSAKA and KOBE Harbors and became the main strength of mine sweeping. They were engaged in mine sweeping in channels where the mines were reported to have been laid.

    2. The status of the strength of mine sweeping units as of 11 June.

      (1) Mine sweeping equipment.

Name Drag net Type 5 mine sweeper Type 3 model 2 mine sweeper Reformed type 3 sweeping equipment Sound bombs
OSAKA Naval Munition Department   7 sets (no accessories) 11 sets Magnetic Bars 940   1,300
KII Defense Garrison 10 (length 10 cm. breath 70 cm. mesh. 6 sq. ft. Manila hemp 1 set (no accessories) 5 sets   130
OSAKA Port Defense Garrison     10 sets   300
KOBE Port Defense Garrison   All equipment lost by fire 22 sets (only 17 sets usable)


      (2) Mine sweeping vessels.

      Name Type 5 Type 5 Model 2 Type F
      KII Defense Garrison Mother boats (converted subchaser) 3
      Side boats (fishing boats) 9
      Fishing boats 10  
      OSAKA Port Defense Garrison   Fishing boats 10
      Schooner 1
      KOBE Port Defense   Fishing boats 12
      Garrison Schooners 1

    1. Set up anti-mine lookout posts in early part of June at important points along the channels to be swept and endeavoured to collect accurate informations quickly.

    2. Planned to set up search lights in the vicinity of AKASHI SETO in order to ascertain the positions of mines dropped. However, the plan did not materialize.

  1. Navigation Control.

    1. Put into effect the navigation control in accordance with the conditions of mine laying and mine sweeping.
        Chief control station: OSAKA Minor Naval Station.
        Other control stations: OSAKA Naval Office of Resident Officers.
        KOBE Naval Officer of Resident Officers.
        KII Defense Garrison.

      When the bombing by U. S. planes became frequent, the time of incoming and outgoing vessels to and from ports was controlled.

    2. As the damage due to bombing and mines grew larger and the navigation of vessels in general (steel) became actually impossible, impetus was given to the use of schooners instead and were actually used. In order to assure the safe-sailing of these vessels, connecting bases were established at six localities; SAKAGOSHI, IESHIMA, SHIMOTSU, TANABE, SUSAMI and URAQAMI.

    3. In order to protect the sailing of vessels, fairway-buoys were planted 2,000 meters apart on one side (partly both sides) of important channels during middle of July.

Number of Dropped and Disposed Mines

  1. Number of times of mine dropping:
    May 5 Times
    June 7   "
    July 4   "
    August 3   "     (Reported)
    Total 19 Times

  2. Estimated number of the dropped mines
    Approximately 500 to 600

  3. Disposed Mines
    By Type 5 mine sweeping apparatus 24
    By Type 3 improved style mine sweeping apparatus 13
    By Acoustic (Sound Bomb) mine sweeping apparatus
      (Includes 15 by use of planes)
    By self or induced explosion 56
    Total 163


Status of Ship Movements and its Effect on the War

  1. Monthly data of the movements of the sea going vessels.

    Month Number of vessels
    OSAKA Port KOBE Port
    Outgoing Incoming Outgoing Incoming

  2. Effects on the war.

    The ships' movements, as noticeable in the above data, were greatly hindered as the result of the magnetic mine laying by the American planes. As its counter-measure, the use of wooden schooners was adopted, but this, too, was threatened even before it could be put to practical use, by the American bombings carried out against our shipping since August.

    Simultaneously with the above measure, the strengthening of our railway transportation was also carried out, but the total capacity of land and sea transportations was so affected that it became a great obstacle in carrying on the war. Such was the general status of our transportation up to the conclusion of war."

    In addition to the above report the following information was submitted under separate cover.

    1. Detailed list showing location and methods used for each mine swept in OSAKA Area.

    2. Chart showing location of all vessels sunk in the OSAKA Area.

    3. List of all vessels sunk or damaged in OSAKA Area.

    4. Reports by individual ships of damage received from mines.


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Transcribed and formatted for HTML by Charles Hall, HyperWar Foundation