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Interrogation Nav 11, Captain Atsushi Oi

18 Oct 1945


OI, Atsushi, Captain, I.J.N.

OI's 25 years of Naval service included training at the Naval War College and numerous assignments to staff duty. He acquired thorough familiarity with the Japanese organization for control and protection of shipping during World War II through his work on the Staff of Combined Escort Forces from its organization in November 1943 until the war's end.

Bureau of Personnel, Navy Department TOKYO March 1941-March 1943
Staff, 21st Minor Base Force SOERABAJA 23 March 1943-25 June 1943
Naval General Staff TOKYO 2 July 1943-14 November 1943
Staff, Combined Escort Forces TOKYO 15 November 1943-21 September 1945
Bureau of Military Affairs, Navy Department TOKYO 22 September 1945



18 OCTOBER 1945

Interrogation of: Captain OI, Atsushi, IJN, a permanent officer of the Japanese Navy who has had staff college training. He served as a Staff Officer of the Combined Escort Fleet from its organization in November 1943 until the war's end.

Interrogated by: Captain Steadman Teller, USN.


Control of Japanese shipping was divided among the Army, Navy and the Transportation and Munitions Departments. Organized naval control of escort and routing was first undertaken seriously with the creation of the independent Combined Escort Fleet in November 1943, following serious losses to submarines and aircraft in the BISMARK ISLANDS and approaches there to. The Combined Escort Fleet was placed under the command of the Combined Fleet in August 1944 when U. S. submarines and air attacks threatened to completely disrupt Japanese shipping in the SOUTH and EAST CHINA SEAS. This reorganization, however, did little to improve the situation which continued to deteriorate steadily.

During the first years of the war, submarine attacks caused most of the losses. In 1944, carrier aircraft raids on shipping concentrations took heavy toll, particularly in tankers. Air and submarine attacks in the SOUTH and EAST CHINA SEAS during early 1945 forced abandonment of convoys between the EMPIRE and Southwest Area in February and the complete stopping of shipping on this route in March. Mining caused some losses at BALIKPAPEN, SOERABAJA, SINGAPORE and SAIGON. Mining by B-29s closed SHIMONOSEKI Strait for two weeks in May 1945.


Q. Who was responsible for directing the routing of Japanese merchant shipping between the homeland and the Southern PACIFIC?
A. I think no definite person was responsible for shipping. The Navy, the Army, and the Transportation and Communication Department were each responsible, and since the Munitions Department was initiated it also has had a strong voice in the matter. These, together in conference when necessary, decided how to arrange the shipping. Our headquarters, the Combined Escort Fleet, were solely responsible for protection. Under the supervision of the Transportation Department there is an organization -- half civil, half governmental -- called the Shipping Control Board.

Q. Did the Shipping Control Board exist throughout the entire war?
A. I don't think so; I think from sometime since 1942 or 1943.

Q. The Shipping Control Board and the various other agencies which you mentioned decided where the ships were to be used, is that correct?
A. Yes, I think so.

Q. After they had decided where the ships were to be employed, who gave the sailing orders from port to port?
A. In the case of Army shipping which was principally transport or transport cargo, the local Army headquarters gave the sailing orders. There was an Army headquarters for shipping at UJINA and several sub-headquarters in various outlying areas.

Q. In the case of shipping controlled by the Navy, who gave the sailing orders to individual ships or groups of ships?
A. We have in the Navy Department a bureau called Naval Transportation Headquarters, which issues shipping orders for all naval supply shipping except ships of the fleet train and naval auxiliaries which are under control of the Combined Fleet.

Q. Did the Combined Fleet have sub-headquarters at various important ports?
A. In the South Sea Area shipping sub-headquarters were located under the various area fleet headquarters. The Combined Fleet ordered shipping through these headquarters only for fleet operational purposes. The Navy Department Transportation Office exercised control over the shipping sub-headquarters for normal shipping. For the most part this was done directly, but it was also done through the area fleet headquarters.

Q. When did the Combined Escort Fleet cease to be independent and become subordinate to the Combined Fleet, and why was that change made?
A. It was the 3rd of August 1944. Because your attack was getting so severe that the entire area even in SOUTH or EAST CHINA SEAS was dangerous. Without assistance of the Combined Fleet we could not protect sea lanes any more.

Q. Prior to August 3, 1944, what resources in escort vessels did the Combined Escort Fleet have?
A. The Combined Escort Fleet had under its command at naval bases and subnaval bases in JAPAN a certain number of old destroyers, PT boats, and sub-chasers for use as escorts. The First Escort Fleet had a certain number of old destroyers and sea defense vessels. Also under the command of the Combined Escort Fleet there were a number of aircraft which were based at TATEYAMA, OKINAWA, TAKAO, MANILA and for a time at SAIGON. The aircraft were largely medium bombers engaged in anti-submarine patrols.

Q. After 3 August 1944, what additions were made to the force available for escorting ships?
A. The area of responsibility of the First Escort Fleet had been the area from JAPAN to SINGAPORE, including the PHILIPPINES and CHINA Coast. Prior to being placed under the Combined Fleet, the Combined Escort Fleet cooperated with the area and expeditionary fleets in the South Seas for escort work, but this cooperation took place only on the highest echelon between the Combined Escort Fleet headquarters and the Combined Fleet headquarters. Each office was able to issue orders only to fleets specifically under their command. After the third of August 1944, the Combined Escort Fleet issued orders directly to the area and expeditionary fleets in the South Seas as well as to the First Escort Fleet, in matters of convoy escorting.

Q. Were the vessels of the expeditionary fleets and area fleets assigned permanently to escort duty or were different ships used from time to time.
A. After August 1944, escort vessels belonging to the area and expeditionary fleets were practically always used on orders from the First Escort Fleet. However, they remained attached to units to which they had been previously attached and were serviced and supplied by those same units. The reason for their availability to the First Escort Fleet was largely that other than escort there was no real need for them at all.

Q. In Western NEW GUINEA and the CELEBES Area, between March 1944 and October 1944. what was the most effective United States form of attack against shipping?
A. I thing submarines were the worst. Anyway up to the end of last year (1944) subs were the most terrible attack force; after that time the air force was. However, the Task Force air raids on TRUK in February and PALAU at the end of March 1944 did terrible damage.

Q. What effect did the Carrier Task Force raid on TRUK on February 17, 1944 have on merchant shipping?
A. At that time we lost several big tankers, some of them over 20,000 tons. Merchant ship losses at TRUK and in the SOUTH CHINA SEA during February 1944 were the greatest losses for any month of the war, and the loss in the TRUK raid amounted to approximately half of the total for the month.

Q. What effect on shipping did the carrier raids on PALAU at the end of March 1944 have?
A. This time also, tankers were chief victims. Not so many were lost as at TRUK, but it was most vital damage. So far as movement or operation of the Combined Fleet was concerned, the loss of tankers in these two raids was very serious. It also influenced the transportation of oil from the NETHERLANDS EAST INDIES to the EMPIRE.

Q. When was the Combined Escort Fleet created?
A. The Combined Escort Fleet was originally organized on the 15th of November 1943 because of the very heavy losses which occurred to shipping in the general area of the BISMARKS where escorts had not been adequate or well organized.

Q. What caused those losses? Submarines, air or surface action?
A. These losses were largely due to submarines. Of course I can't remember exactly. I think, also, air force attacks were most terrible.

Q. In the area of the MOLUCCAS and CELEBES in the summer of 1944, were night air attacks against shipping troublesome? If so, what effect did they have on shipping and escort?
A. Of course they were troublesome, but we did not have so much shipping there. We very quickly abandoned that area. We transported many troops from MANILA to HALMAHERA passing south of MINDANAO, and lost many ships in the CELEBES SEA. Submarines were most dangerous.

Q. After August 1944 did you have enough escort shipping to move your vessels as fast as you wanted to?
A. The supply of the escort vessels available to the Combined Escort Fleet after 3 August 1944 was less than prior to that date. The change in organization at that time was initiated by the Combined Fleet, and the Combined Escort Fleet did not think at that time that from their point of view it was a good change. It meant that their vessels could be used by the Combined Fleet for offensive and defensive operations. We had insufficient force of escort throughout the war and the organizational change of 3 August 1944 did not improve the situation. Furthermore, during the carrier attacks on FORMOSA in October 1944, aircraft suitable for scouting and anti-submarine patrol were practically eliminated. Prior to the organizational change in August 1944, these aircraft for anti-submarine patrol were for the exclusive use of Combined Escort Fleet and could not be used in offensive operations by the Combined Fleet.

Q. When did the aircraft attacks against your shipping in the SOUTH CHINA SEA first become very serious?
A. As I recall, the first time was the carrier attack on January 12, 1945 off CAMRANH Bay.

Q. What form of air attack was considered most dangerous to shipping?
A. I think the carrier air force attack was most dangerous; torpedo attack was most vital, next divebombing and strafing was most dangerous. But single plane attacks against our anti-submarine planes had a very serious effect, because we depended very much on those anti-submarine planes and those planes were shot down and gradually diminish in strength.

Q. In the SOUTH CHINA SEA, carrier attacks occurred only in January 1945. Those carrier attacks were made on SAIGON, HONGKONG, and TOURANE. Do you know how many ships were lost to those carrier attacks?
A. I am not certain but I think more than ten tankers were lost at TOURANE and SAIGON on the same day, and about five or six tankers were lost in HONGKONG a few days later. The first day in HONGKONG there wasn't very serious damage but on the second day all shipping (mostly tankers) was annihilated.

Q. When air attacks along the CHINA Coast drove the shipping to the channels inside of the small islands, did that increase losses due to grounding or have other serious effect on shipping?
A. There was not very much increase in losses due to accident, but we were more easily caught by submarines and airplanes. At that time in March 1945, we thought passing through CHINA SEA extremely difficult, and on the 15th of March abandoned all shipping between the EMPIRE and Southwest Areas. About the end of February 1945, attacks by single planes on shipping in the SOUTH CHINA SEA became very effective in addition to submarine attacks, because we had decided to abandon the use of convoys after your force came to LINGAYAN, and ships were sailing singly.

Q. Are you acquainted with the damage done to merchant shipping by carrier raids in the MANILA Area in September 1944?
A. If I remember correctly we had anchorages in CORON Bay and all along the west coast of the PHILIPPINE ISLANDS; for instance off SANTA CRUZ and other places on the west coast of LUZON. We thought at first that CORON Bay was safe from your carrier attacks. If we took the convoys far into sea we were attacked by submarines, so we took ships into CORON Bay believing it was safe. But your force reached there and I think we received great damage.

Q. Was there a major portion of your shipping in the PHILIPPINES at that time?
A. Those ships were mostly used for supplying and reinforcements of Army garrisons. Our convoys usually took the coast route. Before the carrier raids on MANILA in September 1944, we considered the route FORMOSA, LUZON, PALAWAN, West BORNEO, SINGAPORE was safest because we could protect shipping with aircraft stationed at points along this route. Therefore we had some tankers and ships loaded with bauxite in MANILA Bay. We lost those precious ships as well as Army transports in those carrier raids.

Q. Of the tankers which were repaired in SINGAPORE and sent north to the EMPIRE in early 1945, how many were lost on the way?
A. We lost about 15 percent in February 1945, and beginning of March we lost 30 percent.

Q. During the war, what changes in the armament of escort vessels and merchant ships were made to improve their defense?
A. The most important change was the fall of 1944 when the best Army transport ships were equipped with radar. At the end of January 1945, 25 mm machine guns were drawn from every possible place on shore and even off merchant ships to increase the armament of tankers running from SINGAPORE to the homeland. The plan to increase the armament of merchant ships had been in existence from the beginning of the war, but production was not sufficient to make it possible to carry out the plan. Escort vessels were equipped with radar as much as possible beginning about September 1944. Previous to that only a few escort ships had radar and radar production was mostly for combatant ships.

Q. Did the radar installation include receiving equipment for our radar signals?
A. Radar intercept receivers were on most escort vessels by about April 1944, but this was not very effective because there was no way of locating in bearing and distance. This was principally a warning device. Due to rapid improvement and research, there was sufficient radar for most escort vessels by December 1944.

Q. What did you consider the most effective weapon against the submarine -- aircraft or escort vessel?
A. Planes equipped with radar; especially those equipped with MAD.

Q. How many American submarines did you estimate were sunk?
A. It was very difficult to determine, but the Navy's estimate was 16 per month.

Q. Were your communications adequate for conducting the business of escort, routing and protection of ships? If not adequate, in what way?
A. Communications caused a great deal of trouble. There was great delay due to lack of facilities on most merchant ships, inadequate facilities on escort vessels, and no direct communications between escort vessels and aircraft. Communication among headquarters and commands were also frequently delayed. This was considered a weak point.

Q. Before the B-29's dropped the mines in JAPAN waters in the beginning of April 1946, did the mines we laid in BORNEO, PHILIPPINES and along CHINA Coast affect merchant ship planning?
A. I think we hadn't been affected very much in the SOUTH CHINA SEA. We suffered very much at BALIKPAPAN and we abandoned the route from BALIKPAPAN to SINGAPORE.

Q. Because of mines only?
A. It was abandoned chiefly because of mines, but also because of planes attacking from MOROTAI. This was about December 1944.

Q. Do you know how many ships were lost by mines at BALIKPAPAN? Were the losses so great you were forced to abandon the port?
A. We didn't abandon the port just because of mines, because BALIKPAPAN was very important to us. In December 1944, however, due to the combined effect of mines, subs and air attack, BALIKPAPAN was officially abandoned.

Q. What losses were suffered at SOERABAJA?
A. I can't remember the number of vessels lost. Anyway our transportation from SOERABAJA was suspended for a long time. We would sweep the channel and one or two ships could get out or go in and then your forces would mine it again. Finally I think only very few small ships could use this port.

Q. Were the major losses suffered from mines in the South Area at SOERABAJA and BALIPAPAN?
A. Major losses suffered in the Southern Area were at SOERABAJA, SAIGON, and SINGAPORE and along the east coast of MALAYA.

Q. After the mining campaign was under way in JAPAN, did conditions get so bad that it was necessary to pass ships through the minefields knowing full well they would be lost?
A. Yes. We took this chance, especially in SHIMONOSEKI Strait.

Q. Do you know whether or not the mining in the INLAND SEA affected the movement of the YAMATO when it reinforced operations at OKINAWA?
A. It didn't affect it very much.

Q. How long was SHIMONOSEKI Strait closed?
A. SHIMONOSEKI Strait was closed for a period of two weeks in the middle of May and only wooden vessels less than 100 tons were able to pass through.

Q. Did you fear the possibility of damage to the tunnel by mines?
A. Yes, we feared that very much. It was not actually damaged, but we were afraid. ww2dbase

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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