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Interrogation Nav 59, Rear Admiral Akira Matsuzaki

30 Oct 1945


MATSUZAKI, Akira, Rear Admiral I.J.N.

MATSUZAKI was a regular officer with 30 years experience. As Chief of Staff of the Southern Expeditionary Fleet at SOERABAJA and later as Chief of Staff of OSAKA Naval Station he had an opportunity to become very familiar with the defensive phases of mine warfare. He was extremely cooperative and made every effort to furnish in accurate detail all information requested.

Officer in Charge, 1st Section General Affairs Section, Naval Technical DepartmentTOKYONovember 1942-April 1943
Chief of Staff, Second Southern Expeditionary FleetSOERABAJAApril 1943-February 1945
Chief of Staff, OSAKA Naval StationOSAKAFebruary 1945-August 1945



30 OCTOBER 1945

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 FleetFirst 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 sweepers2 units
       Type 3 model 2 mine sweepers3 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.
        NameDrag netType 5 mine sweeperType 3 model 2 mine sweeperReformed type 3 sweeping equipmentSound bombs
        OSAKA Naval Munition Department 7 sets (no accessories)11 sets Magnetic Bars 940 1,300
        KII Defense Garrison10 (length 10 cm. breath 70 cm. mesh. 6 sq. ft. Manila hemp1 set (no accessories)5 sets 130
        OSAKA Port Defense Garrison  10 sets 300
        KOBE Port Defense Garrison All equipment lost by fire22 sets (only 17 sets usable)
      2. Mine sweeping vessels.
        NameType 5Type 5 Model 2Type F
        KII Defense GarrisonMother 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
    3. 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.
    4. 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.
  4. 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:
    August3"    (Reported)
  2. Estimated number of the dropped mines
    Approximately 500 to 600
  3. Disposed Mines
    By Type 5 mine sweeping apparatus24
    By Type 3 improved style mine sweeping apparatus13
    By Acoustic (Sound Bomb) mine sweeping apparatus
    (Includes 15 by use of planes)
    By self or induced explosion56

Status of Ship Movements and its Effect on the War

  1. Monthly data of the movements of the sea going vessels.
    MonthNumber of vessels
    OSAKA PortKOBE Port
  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.

Source: United States Strategic Bombing Survey (Pacific) Interrogation of Japanese Officials [OPNAV-P-03-100], courtesy of ibilio Hyperwar Project
Added By: C. Peter Chen

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