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Chapter II
Japanese Arrangements(a) JAPANESE COMMAND RELATIONS (Plate I)
All of the Japanese Fleets, including the Naval Air Fleets, excepting the China Seas Fleets, were under the Command of the Commander-in-Chief of the Combined Fleet. The Combined Fleet consisted of the mobile (mission) fleet which could operate anywhere in any area, and of the localized (area) fleets which were responsible for and restricted to certain geographical areas. The mobile fleet constituted the main striking force of the Combined Fleet. The area fleets were normally defensive in character and were generally unable to take any strong offensive action without assistance from the mobile fleet.* The mobile fleet consisted of the Main Body (First Division FIRST Fleet), the Advance Force (SECOND Fleet), and the Striking Force (THIRD Fleet),** the area fleets consisted of the Northern Force, later called Northeast Area Force (FIFTH Fleet) based at Horomushiro; the Inner South Seas Force (FOURTH Fleet) based at Truk, the Outer South Seas Force (EIGHTH Fleet) based at Rabaul and the Southwest Area Force (Combined Expeditionary Fleet) based at Surubaya.** In addition to the mobile fleet and the area fleets, the Combined Fleet consisted of the Base Air force (ELEVENTH Fleet) base on Tinian and the Advanced Expeditionary Force (SIXTH fleet) which was composed of submarines and was based at Kwajalein.** All tactical titles employ the term "Fleet" with the single exception that the title "Combined Fleet" was both administrative and tactical (Plate I)***
Prior to July 14th, 1942 the South seas Force was responsible for the defense of the Central and southeastern Pacific Area, including the Marshalls, New Guinea, and the Solomon Islands. However, due to the increasing importance of the Central and southeastern Pacific Areas and to the fact that there was an ever-increasing threat of an attack on the Solomons by the Allies, the Japanese High Command decided to split the South Seas Area into two areas, one, an Outer South Seas Area, the other, an Inner South seas Area. This split became effective on July 14th, 1942.****
The dividing line between the two areas thus formed was established as the line bearing 280°(T) from the juncture of the equator and Long.
* Japanese Naval Organization, Change No. 11 to ONI 49, page 5.** Enclosure, Submitted October 26th, 1945 by Rear Admiral Nakamura, IJN, in answer to USSBS Memorandum No. NAV-1, October 10th, 1945.
*** Japanese Naval Organization, Change No. 11 to ONI 49, page 33.
**** War Diary, 8th Fleet, August 7th, 1942, WDC Document 161259.
150° E. Commander Inner South Seas Force was assigned the responsibility for the defense of the area north of this line and Commander Outer South Seas Force for the defense of the area south of this line. In order to provide for unity of command, it was directed that in the event of an enemy attack in the above areas, the Commander ELEVENTH Air Fleet would, in case of necessity, exercise over the FOURTH, SIXTH, AND EIGHTH Fleets.*Vice Admiral Gunichi Mikawa activated the EIGHTH Fleet on July 14th. On July 16th he hoisted his flag in the Chokai. On July 23rd he was assigned the Chokai and Cruiser Division SIX and became Commander Outer South Seas Force. On July 27th he formally assumed responsibility for the New Guinea and Solomon Islands operations.*
All land based air forces in this operation wee naval and were assigned to the FIFTH Air Attack Force** (25th Air Flotilla), which was based at Rabaul and was a subdivision of the ELEVENTH Air Fleet. The Commander of this attack force retained operational control over his component un its and cooperated with the Commander Outer South Seas Force. He remained at Rabaul to direct its activities. No Army air forces were assigned at this time.***
Vice Admiral Mikawa was in command of the Outer South Seas Force until about 1415, August 7th when he was relieved by Vice Admiral Nishiso Tsukahara, who was the Commander Base Air Force and the Commander ELEVENTH Air Fleet. The latter admiral acted as Commander Outer South Seas Force which included the Base Air Force, the Inner and Outer South Seas Forces, and a portion of the Advanced Expeditionary Force.*** In this latter capacity he was the Immediate-Superior-in-Command of Commander EIGHTH Fleet.
It therefore happened that at the time of the Allied landings on Guadalcanal and Tulagi on August 7th, Vice Admiral Mikawa was both Commander Outer South Seas Force and Commander EIGHTH Fleet.** After he had been relieved by Vice Admiral Tsukahara he had the primary responsibility of securing a victory with his surface force.
From the above, it is evident that, although the Japanese command structure had room for confusion, there was no confusion in command in the battle of Savo Island. All forces wee engage naval forces, and all were under the direct command of naval officers in a clearly defined chain-of-command.
* War Diary 8th Fleet, August 7th, 1942, WDC Document 161259.** Records 25th Air Flotilla, CIG Document 74629, May 12th 1947.
*** War Diary 25th Air Flotilla, August 1942, WDC Document 161730.
Plate I: Japanese Command Relations on 8 August 1942
(b) INFORMATION AVAILABLE TO JAPANESE COMMANDER
Just prior to the Allied landing in the Solomons, Commander South Seas force had considerable general information concerning the strength of the Allied forces in the south Pacific area, and was generally aware of their capabilities.
He knew that there had been considerable Allied air and naval activity in the general area of the Coral Sea and that there was a possibility of an early engagement with a powerful enemy force.*
He was aware of the Allied construction of and build-up of bases in New Caledonia and New Hebrides.Interpreting this activity as a preparation for a counterattack upon Japanese advanced positions, he correctly assumed that the most likely area of allied counterattack would be the southern Solomons.**
He knew that the Allied forces had reconnoitered the new base at Guadalcanal-Tulagi frequently by air and that the number of planes raiding that area had suddenly increased during August.***
Informed by his intelligence that a powerful Allied force had sortied from Hawaii on August 2nd, he suspected that this force together with other Allied forces already in the southwest Pacific Area, would attempt to attack the Outer South Seas Area in the near future. He understood that this combined force would include three carriers (including converted carriers), and a number of cruisers.**** This Japanese intelligence was reasonably correct, except that the "powerful Allied force" had sortied from Fiji on August 1 rather than from Hawaii on August 2nd, and was at that date much closer to the Solomons than the Japanese expected.
Regardless of how powerful this allied force, he believed that he might be able to intercept and destroy it by decoying it within range of his land-based naval air power.*** He felt that he might accomplish this even without carrier task force assistance from the Combined fleet.**** This concept of destroying American surface forces by land-based planes was not new. The Japanese had held the same concept at the battle of Midway when they endeavored to lure the American carrier force within
* War Diary 8th Fleet, August 7th, 1942, WDC Document 161259.** War Diary 8th Air Attack force, August 1942, WDC Document 161730, and CRUDIV 6 Detailed Battle Report #8C, August 7th-10th, 1942, CIG Document 86927, June 27th 1947, page 2.
*** Southeast Area Naval Operations, Part 1, document 40427, page 10, Historical Division, U.S. Army, July 31st, 1947.
**** War Dairy 8th Air Attack Force, August, 1942, WDC Document 161730 and Commander 8th Fleet Estimate of situation, August 7th, 1942, CIG Document 73846, May 7th, 1947, page 1.
range of Japanese land-based air power at Wake. It showed a confidence that their land-based air power was more effective then American carrier-based air power--a confidence that was not borne out throughout the war.He knew that the enemy had recently assembled great air strength in the New Hebrides area and he considered that the enemy was planning to invest Guadalcanal before the Japanese air strength moved up.*
In anticipation of this latter possibility, he had recommended, in his capacity of commander EIGHTH Fleet, that a planned withdrawal of a cruiser division from Rabaul to Truk be modified, and that it should be sent to Kavieng or to Queen Carola Harbor.* This action was taken, and that CRUDIV SIX was held in the Kavieng Area as a support force of the Outer South Seas Force Area
He knew that larger numbers of enemy submarines were beginning to infest the waters of Japanese Southeast Area Force, necessitating the diversion of additional escort forces to this area. He considered it probable that this enemy submarine activity would become increasingly intense.**
He knew that CINCPAC was in the Hawaiian Area and that COMSOWESPAC was located in Brisbane. There is however, no indication that he was aware of the formation of SOPAC which was soon to undertake and direct an assault in the Guadalcanal-Tulagi Area.***
Finally, it is highly probable, in view of his visit to Truk (July 25th-26th) and his discussion there with the CINC Combined Fleet concerning the operation in the Outer South Seas Area,* that he was familiar with and generally concurred with the Imperial Headquarters opinion that from the extent of enemy preparations particularly in carriers, that any enemy counterattack would probably be no more than a reconnaissance landing.****
(c) JAPANESE LAND AND TENDER-BASED AIRCRAFT
All Japanese aircraft employed in the operations in the Solomons, incident to the Battle of Savo Island, were naval aircraft of the 25th Air Flotilla. The Commander of this air flotilla, with headquarters at Rabaul, was directing activities of the FIFTH Air Attack Force, Base Air
* War Diary 8th Fleet, August 1942, WDC Document 161259.** CRUDIV 6 Detailed Battle Report, Solomons Naval Action, August 7-10th, 1942, WDC Document 160997.
*** War Diary 5th Air Attack Force, August 1942, WDC Document 161730.
**** Southeast Area Naval Operations, Part I, Document 40427, page 10, Historical Division, U.S. Army, July 31st, 1947
Force.* The 25th Air Flotilla constituted that part of the Base Air Force which was located in the southeast area. Its composition on August 6th is shown on Table 1, and totaled 113 planes of various types. The units involved in this organization were the TAIMAN air Group, the SECOND Air Group, the YOKOHAMA Air Group, the FOURTEENTH Air Group, and the FOURTH Air Group.* Two special duty units (surface ships capable of serving as tenders for reconnaissance and fighter seaplanes) were attached to the 25th Air Flotilla. These were the seaplane carrier Akitsushima, Special Duty Unit ONE, and the aircraft transport Mogamigama Maru, Special Duty Unit TWO.* On August 7th and 8th, thee 25th Air Flotilla was expanded by the addition of planes of the MISAWA Air Group.**The land-based planes of this flotilla, as yet unequipped with radar, were disposed between the Vunakanau and Lukanai Airdromes at Rabaul. The seaplanes were disposed at both Rabaul and Tulagai. The Tulagai planes were stationed there to protect the Guadalcanal Air Base wile it was under construction.**
Additional airfields throughout the Solomons were needed by the Japanese and for the purpose of building them Naval construction battalions were placed under the command of the Base Air Force.** Two airfields had been rushed to completion, the Guadalcanal Air Base which was finished on August 6th and an airfield at Buka Passage, which was ready to operate as a base on August 8th. Neither of these two bases had been assigned air groups at the time of the Battle of Savo Island. The Commander ELEVENTH Air Fleet and Commander 25th Air Flotilla had dissuaded Commander Outer South Seas Air Force from his desire to move up land attack units immediately upon completion of Guadalcanal Air Base for the reason that there was inadequate air strength, as yet, at Rabaul to permit such disposition.***
Until land bases were available, suitable harbors for basing patrol and fighter seaplanes were needed. The Japanese bad selected harbors for seaplane bases at Faisi, Shortland Island, Buka Passage, Giso Island, Kieta (Bougainville Island), and at Rekata Bay (Santa Isabel Island). No air activity was noted in these harbors by COMSOWESPAC air reconnaissance on August 5th, 6th, 7th, or 8th.
The employment of Navy land-based aircraft, other than Army aircraft, in the Southeast Area was in accordance with Japanese practice. It was necessary, in part, because Japanese Army air groups were not trained in the conduct of Joint Operations with naval air forces.****.
*Strength and disposition of 25th Air Flotilla on August 7th 1942, CIG Document 74629, May 12th 1947, and War Diary of 25th Air Flotilla, August 1st-31st, 1942, WDC document 161730.**Records 25th Air Flotilla, Item 21D, Section 3, June 25th to August 6th, 1942, WDC Document 160155.
***Southeast Area Naval Operations, Part I, Document 40427, page 10, Historical Division , U.S. Army, July 31st, 1947.
****Japanese answers to 08586 Military Division Questionnaire #1.
Since the commencement of the war, naval aircraft had been highly successful in spear-heading Japanese naval attacks. The Japanese now expected their naval aircraft to be equally successfully in the Solomon operations*
(d) JAPANESE SEARCH AND RECONNAISSANCE
The Japanese did not detect the Allied Expeditionary Force as it was advancing northward along the meridian of 159° E. Longitude toward Tulagai and Guadalcanal on August 5th and 6th. No searches through the Solomons sector were flown on those two days from Rabaul, reportedly because of bad weather.** COMCRUDIV SIX reported that weather also prevented the Japanese Reconnaissance seaplanes at Tulagai from locating the Allied Force.*** There is reason to believe this statement since the area the Allied Force traversed in its approach to the objective was not searched by the Allied B-17's either on August 5th and 6th.**** (The movement of the Allied Force is shown on diagram "B" and passed through SOPAC Search Sector I). However, weather did not prevent the Allied carriers in the Allied Support force from conducting routine local security patrols on these same two days.*****
The Japanese were caught by complete surprise on August 7th by the Allied Expeditionary Force, even though the High Command had directed their units in the South Pacific on August 5th to exercise strict caution.****** Although he had been advised by his air commanders that his air strength at Rabaul was inadequate,** he nevertheless gave considerably less attention to the Solomons sector than he did to the New Guinea sector. This resulted in inadequate searches in the Solomons sector prior to the Allied landing on August 7th.
The land attack planes at Rabaul were heavily engaged in almost daily bombing attacks on the Allied air bases at Port Moresby. Additionally, Commander FIFTH Attack Force was employing a few land attack planes for reconnaissance in connection with the New Guinea offensive operations******* and for reconnaissance flights to locate possible base sites
* War Diary, 6th Fleet, August, 1942, WDC Document 161259.** Southeast Area Naval Operations, Part I, Document 40427, page 10, Historical Division, U.S. Army, July 31st 1947.
*** CRUDIV 6 Detailed Battle Report #6, Solomons Naval Action, August 7th-10th, 1942, WDC Document 180997.
**** War Diary COMAIRSOPAC (CTF) 63, August 1942.
*****War Diary Saratoga, August 1942.
****** War Diary 1, "A Brief History of World War II(B) No.1 December 1941 to March 1943", page 12, Supreme Commander of the Allied Powers, AFIS Document WW 16266.
******* Records 25th Air Flotilla, Group 21, Item 21D, Section 3, June 25th to August 6th, 1942, WDC Document 160155.
The Louisiades and D'Entrecastraux Islands.* He relied largely on the seaplanes of the YOKOHAMA Air Group, based at Rabaul and Tulagai, for reconnaissance of the Solomons Sector and of the approaches to Tulagai from the southeast.* His search planes at Tulagai, as was pointed out in the previous section of this analysis, were sent there to conduct reconnaissance for the protection of the Guadalcanal Air Base.* It is probable, therefore, that his reliance on the search planes operating out of Tulagai gave the Commander Outer South Seas Forces a confidence not warranted by the situation, and that this confidence contributed greatly to the surprise achieved by the Allies.The routine Japanese air searches scheduled for August 7th were to be conducted by seaplane only. Those at Rabaul were to cover a sector between bearings 100° (T) to 130° (T) to a radius of 700 miles,** those at Tulagai were to cover an unidentified sector to the southward of the Solomons. The latter seaplanes were caught on the water at dawn by Allied carrier planes and were destroyed before they could take off.***
The contact report of the Allied Expeditionary Force received from Tulagai Air Base at 0652, August 7th, precipitated an immediate change in Japanese search plans. As will be shown later, Commander Outer South Seas Force requested the FIFTH Air Attack Force to augment the seaplane searches by the employment of land attack planes based at Rabaul. The Japanese thereby demonstrated a capability of increasing very considerably the number of aircraft employed for searching the Solomons. It is unfortunate for them that these augmented searches were not initiated on August 5th when the warning came from the High Command.
(e) JAPANESE DISPOSITION NAVAL FORCES
Just prior to the surprise Allied invasion of the Guadalcanal-Tulagai area the Japanese forces of the Southeast Area were disposed in accordance with the strategical situation as it appeared to the Japanese commanders at that particular time. The EIGHTH Fleet was operating from Rabaul as a principle naval base. Since Rabaul was at this time under the constant harassment and surveillance of Allied air power based in Australia and staging through Port Moresby, Commander EIGHTH Fleet was inclined to favor the more northerly harbor of the area, Kavieng, as an anchorage for his surface forces. As a consequence, on August 1st, he dispatched the heavy cruiser Chokai, the flagship of the EIGHTH Fleet, and Cruiser Division SIX, consisting of the Aoba, Kako, Kinugasa and Furutaka from Rabaul to Kavieng, there to remain until the morning of August 7th.****
* Records 25th Air Flotilla, Group 21, Item 21D, Section 3, June 25th to August 6th, 1942, WDC Document 160155.**Japanese Search Plans, August 7th-9th, 1942, CIG Document 74632 May 12th, 1947.
***Strength and Disposition of 25th Air Flotilla on August 7th, 1942. CIG Document 74529 May 12th, 1947.
****War Diary CRUDIV 6, August 1942, WDEC Document 160997.
TABLE 1
DISPOSITION OF USABLE JAPANESE SHORE & TENDER BASED AIRCRAFT*
as of 2000 August 8th
Base Taiwan Air Group 2nd Air Group Yokohama Air Group 14th Air Group 4th Air Group Misawa Air Group Total Type Zero Shipboard Fighter (ZEKE 11) Type Z Land Recce Plane Type Zero Shipboard Fighter (ZEKE 11) Type 99 Carrier Bomber Type 97 Flying Boat (MAVIS 11) Seaplane Fighter Type Z Large Flying Boat Type 1 Land Attack Plane (BETTY 11) Type 1 Land Attack Plane (BETTY 11) RABAUL **24 2 **15 16 6 2 65 VUNAKANAU
(Rabaul)32 *** 32 TULAGI 7 9 16 TOTAL 24 2 15 16 13 9 2 32 0 113 Total number of Usable Planes Between 0000 August 7th and 2400 August 9th
Type Zero Shipboard Fighter Type 2 Land Recce Plane Type 99 Carrier Bomber Type 97 Flying Boat Seaplane Fighter Type 2 Large Flying Boat Type 1 Land Attack Plane 0000 Aug. 7 39 2 7 13 9 2 32 0000 Aug. 8 37 2 7 6 0 2 36 0000 Aug. 9 34 2 7 6 0 2 27 0000 Aug. 10 34 1 7 6 0 2 24
*None of these aircraft were equipped with radar.**Based at Rabaul and assigned to Lae and Buna, New Guinea, and Tsui Rumi, New Britain areas as fighting progressed.
***Nine land attack planes of this air group reported on August 7th and eight on August 8th, making a total of seventeen additional planes.
NOTE: The above tables are based on CIG Intelligence Report 74629 of 12 May 1947, "Strength and Disposition of Air Flot. 25 on 7 August 1942" and on WDC 160140 "Detailed Battle Report No. 8 of the Fifth Air Attack Force."
He himself remained at his headquarters in Rabaul.
- The disposition and composition of the principal units of the EIGHTH Fleet at 0652, August 7th, the time Commander EIGHTH Fleet received the report of the initial sighting of the Allied Amphibious force (TF 62) by the Japanese at Tulagai, is summarized as follows:
- Support Force and Chokai
The heavy cruisers Chokai, Aoba, and Kako were en route to Seeadler Harbor, Manus Island, Admiralty Islands. The heavy cruisers Kinugasa and Furutaka were en route to Rabaul. All five cruisers had just cleared the southern entrance to Steffen Strait on routine passage from Silver Sounds.*
- Escort Force
- The light cruisers Tenryo and Yubari and the destroyer Yunagi of DESDIV TWENTY-NINE [unreadable] at Rabaul.*
- The destroyers Oite,
Yuzuki of DESDIV Twenty-Nine and the destroyers Mitsuki, Uzuki, Yatoi, and Mochisuki of DESDIV THIRTY were engaged in escort duties. DESDIV SEVENTEEN was ordered to report to commander Outer South Seas Force on August 5th but had not yet arrived at Rabaul. As these destroyers did not partake in the battle of Savo Island, they are dropped from further discussion. - Auxiliaries of 25th Air Flotilla.
The seaplanes [illegible] and the aircraft transport Momigama Maru were at Rabaul.**
- Submarines
- SUBRON SEVEN was located about as follows: RO-33 in Gulf of Papua, RO-34 off Australian East Coast, I-121 and 122 at Rabaul and I-123 at Truk.***
- SUBRON THREE, which reported from the SIXTH Fleet to the EIGHTH Fleet on August 7th, were on station as follows: I-11 off the
*CMDDIV 6 Detailed BattleReport #8, Solomons Naval Action, August 7th-10th, 1942, CIIG Document 86927, June 27th, 1947.**Strength and disposition 25th Air Flotilla, August 7th,1942, CIG Document 74629, May 12th 1947.
***War diary 8th Fleet "Movements of Naval forces under this Command", August,1942, WDC Document 161259
Southeast coast of Australia; I-174, and I-175 off the east coast of Australia; I-169 off the New Hebrides, and the I-138 which had remained at Sasebo, Japan.* SUBRON THREE is dismissed from further discussion, since all boats were ordered on August 7th to return to Japan for rest and refitting. None of them were employed in the Japanese counterattack at Tulagai.
(f) TASKS ASSIGNED
The tasks assigned the EIGHTH Fleet by the Japanese were in general:
- To support the Japanese program of consolidating the network of outposts protecting the Rabaul position, which often required invasion operations.
- To counter successfully the general anticipation of the Allied Offensive against the area.**
The first of these assigned tasks has significance only because the Japanese consolidation of Japanese outposts protecting Rabaul had precipitated the Allied amphibious operations against Tulagai and Guadalcanal. Since the Battle of Savo Island resulted directly from the second assigned tasks, it is that task with which this discussion is concerned.
Commander Outer South Seas Force knew that his objective was protective in nature. He also knew that the principal offensive weapon in his area was the land-based airpower of the FIFTH Air Attack Force (Base Air Force) at Rabaul. This weapon would be most useful to him during high visibility. He considered that its full capabilities could only be exploited against strong enemy sea forces if the latter were within striking distance; and concluded that he might best accomplish this by employing some of his surface forces as decoys to lure the enemy forces within range of such air power.***
He knew that his own offensive power lay primarily in his heavy cruiser strength--the Chokai and CRUDIV SIX--plus any light cruisers and destroyers which could be made immediately available from the convoy escort force. He felt that during high visibility this surface force would be a secondary weapon to the Base Air Force units at Rabaul and would be vulnerable to Allied carrier-based bombers. But, during night or
*Reports of Meritorious Action SUBRONS 3 AND 7, August 10th, 1942. CIG Document 74834 May 12th, 1947.**Records CRUDIV 6, WDC Document 160997, August, 1942, War Diary 8th Fleet, WDC Document 161259, July-August,1942; Southeast Asia Naval Operations, Part I, Document 40427, page 3; and the Campaigns of the Pacific War, USSBS 1946, page 105.
*** War Diary 8th Fleet, WDC Document 161259.
low visibility, he felt that his cruiser force became his principal weapon. The smallness of his force gave him little concern, for he was confident of his ability to defeat Allied surface forces in night action.In addition to his surface forces, Commander Outer South Seas Force had four submarines of SUBRON SEVEN, three of which were available in his area. These sub-surface units might provide some assistance in attacking enemy ships.
The above Japanese capabilities, when considered in comparison with the strong Allied carrier and amphibious support forces sent to Tulagi and Guadalcanal, were limited indeed. The confidence expressed by Commander Outer South Seas Force therefore seems to have been somewhat optimistic. The discrepancy between his appreciation of the assigned objective and [source truncated].
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