Interrogation of: Lieutenant Commander OKAMOTO, T., IJN, a naval aviator. Staff Officer of First Escort Fleet Air Squadron and General Headquarters, Grand Escort Fleet.

Interrogated by: Captain Steadman Teller, USN.


The Japanese Navy first employed an Airborne Magnetic Detecting instrument in antisubmarine warfare during the middle of 1944. The instrument had an effective range of 150 meters under average conditions and 250 meters under ideal conditions. The best height for an aircraft employing MAD was considered to be 10 to 50 meters depending on pilot's skill. Aircraft equipped with MAD were employed principally to sweep ahead of convoys or to exploit a submarine contact made by other means. It was planned to use MAD equipped aircraft to sweep heavily travelled convoy routes, but lack of aircraft and equipment prevented this. It was considered sufficiently reliable to warrant calling in surface craft to an initial contact. (Note: The Naval Technical Mission in JAPAN and Technical Air Intelligence Groups have covered the technical features of this instrument.)


Q. Where have you had operational experience with the Magnetic Detector used in aircraft?
A. In November 1944, we began to employ our MAD between FORMOSA and the PHILIPPINES and at the beginning of 1945 we began to use it between JAPAN and SINGAPORE. The very first experience with the MAD was in March 1944. My experience began in November 1944 with the MAD. We called the instrument JIKITANCHIKI (Magnetic Detector). From November 1944 until March 1945, I was at the headquarters of the First Escort Fleet Air Squadron at TAKAO.

Q. What type of planes were equipped with the MAD?
A. Type 96 land attack planes and Type Zero three-seated, seaplane reconnaissance, Type 97 carrier attack plane and the Tenzan plane.

Q. Was the MAD used as search instrument or as a supplement to other instruments?
A. During the day time, we employed the MAD gear; at night we used radar and radar intercept. The MAD was used in direct support for convoy. We would use it in searching against submarines that might attack the convoy. However, after contact was made with submarine by radar we called in the planes and the MAD is used to plot the speed of the submarines. In addition to direct cover of convoy by this instrument, it was planned to use the MAD to sweep the convoy route from CHUSAN ARCHIPELAGO (just south of SHANGHAI) to SAISHU Island and then to TSUSHIMA and then to SASEBO and SHIMONOSEKI Straits. This cover was to be a strip 30 miles wide.

Due to lack of fuel and planes we were unable to make regular magnetic sweeps; instead, the aircraft were called out if a submarine was found or suspected there and we would commence searching operation with the MAD for that particular submarine. However, at night this route was swept by one radar equipped plane leaving from each terminal and covering the 30 mile width. If planes and fuel had been available, it was planned to use 80 planes to cover this channel with MAD in one day. It was planned to use six simultaneously to patrol this channel. When American submarines forced the Japanese shipping to follow the route from CHUSAN around the shore of the YELLOW SEA, a radar search of the direct convoy route between CHUSAN and the EMPIRE was maintained; but also coverage by MAD planes was given to convoy route along the coast. For this purpose aircraft was stationed at SHANGHAI, CHUSAN, TANSUI (FORMOSA), SHINCHIKU (FORMOSA). The U. S. air attacks on the FORMOSA Area prevented the establishing of sweep routes between FORMOSA and the PHILIPPINES although it was planned to do so. After the U. S. attack practically eliminated shipping through the YELLOW SEA, there was still maintained sweeps in the channel between KYUSHU, SAISHU and TSUSHIMA.

Q. What was the best height for your aircraft to fly when using the MAD?
A. Expert pilots flew at 10 meters; ordinary pilots flew at 50 meters.




Q. What was the range of detection from these heights?
A. Under average conditions trained personnel could detect submarines at the depth of 150 meters from a plane flying from 10 to 50 meters above the surface. The radius range of detection in other direction was approximately 150 meters. However, experienced pilots with equipment in excellent condition and good operating personnel could detect a submarine at a maximum depth of 250 meters.

Q. Describe by diagram the employment of MAD planes in convoy coverage?
A. See Annex A.

Q. What was the procedure when your MAD discovered a submarine?
A. See Annex B.

Q. Can you determine the course of the submarine by tracking with the MAD?
A. Yes.

Q. Was the MAD sufficiently reliable to justify calling in surface craft to develop each contact?
A. Yes. Some difficulty was experienced in contacts with sunken hulks, particularly around the EMPIRE Area. One method of determining that it was a hulk contact was the presence of dead fish which resulted from the depth charge. It was considered that fish would not be found in numbers around a submarine.

Q. Were certain squadrons equipped with and specially trained for the MAD?
A. Yes.

Q. How many aircraft were equipped with this device during the war?
A. The following air groups were assigned to work with convoys and for anti-submarine operations:

GroupArea Number of Planes
903JAPAN 120
951JAPAN 120
901FORMOSA 200

1/3 of these aircraft were equipped with radar.
1/3 of these aircraft were equipped with MAD. (Of these some planes (Type 96 land attack) had both equipments).
1/3 of these aircraft were not equipped with either.

Q. How many sinkings were attributed to MAD?
A. Between August 1944 and July 1945, approximately one year, there were seven submarines sunk in the South Sea Area as a result of the MAD and four in the EMPIRE Area.

Q. How much training was required to produce a group to operate a MAD plane?
A. Three months special training with the equipment.

Q. Was this equipment used for automatic release of depth charges?
A. Just the markers were. The bombs were not.


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Transcribed and formatted for HTML by Charles Hall, HyperWar Foundation