Philippine Sea

The Philippine Sea is a region of the western Pacific bounded by Japan to the north, the Bonins to the northeast, the Marianas to the east, the western Carolines to the south, the Philippines to the southwest, Formosa to the west, and the Ryukyus to the northwest. The ocean floor under the Philippines Sea is a crustal plate distinct from the Pacific plate to the east or the Asian plate to the west.

Battle of the Philippine Sea

The Philippine Sea was the location of the last major carrier battle of the Pacific war, which took place when Toyoda activated the A-Go plan to counter the American invasion of the Marianas in June 1944. Because the American submarine blockade had crippled the Japanese tanker fleet, the Japanese were forced to base their main surface forces close to their sources of fuel in Borneo. The Japanese plan therefore called for a decisive battle to be conducted near the Palaus. Here the Japanese 1 Mobile Fleet under Ozawa would engage and destroy the Americans with the assistance of land-based aircraft.  Should the Americans choose to strike against the Marianas instead, the plan called for the American fleet to be attacked by land-based air only, and lured south into more favorable waters for the Japanese.

A-Go. As it became clearer that the Marianas were a likely target for the Americans, the Japanese Navy took the dangerous step of authorizing the use of unrefined Borneo oil as bunker fuel. This was a desperate measure. Borneo oil was of high enough quality to burn directly in ships' boilers, but it contained enough sulfur to embrittle boiler tubing, and it also had enough volatiles to be dangerously flammable. However, the use of unrefined Borneo oil economized on tankers and made it possible for the fleet to operate at a considerably greater distance from its fuel sources, bringing the Marianas within range for a fleet action.

However, the Japanese continued to hope that the Americans would strike to the southwards, as reflected in their aircraft dispositions. By early June, there were 4 aircraft at Chichi Jima; 35 at Saipan; 67 at Tinian; 70 at Guam; 67 at Truk; 40 at Yap; 134 at Palau; 25 at Davao; 40 at Cebu; 42 at Halmahera; and 16 in western New Guinea. Additional aircraft were available in the home islands and the Netherlands East Indies to be staged in once A-Go was activated, for a total of about 500 land-based aircraft on call for the decisive battle.

The Japanese conducted a number of teishin ("daring") reconnaissance missions in late May and early June that gave them a reasonably clear picture of American dispositions. A reconnaissance flight on 27 May from Truk staged through Buin to Tulagi and gathered accurate intelligence on Conolly's Southern Attack Force. Another pair of aircraft staged from Truk through Nauru to reconnoiter the fast carrier forces at Kwajalein and Majuro. This information pointed to an attack on the Marianas, but Imperial General Headquarters was preoccupied with the Biak landings, which threatened airfields important to the A-Go plan. Operation Kon failed in its first two attempts to relieve Biak, and the third attempt was canceled when Toyoda got word of carrier strikes on Saipan on 11 June, which finally convinced the Japanese leadership that the Marianas were the next American target. On 12 June Toyoda activated A-Go, and on 13 June Ozawa sortied from Tawi Tawi. His force was immediately observed by submarine Redfin.

Part of the Japanese plan called for scouting lines of submarines to cover possible avenues of approach for the Americans. These were almost completely unsuccessful, due largely to the efforts of Allied code breakers, and no less than 17 of the submarines were lost. Not a single submarine was in position to influence the subsequent fleet action.

The Balance Sheet. The Japanese fleet was considerably weaker than the American fleet. The Americans had 7 fleet carriers and 8 light carriers to the Japanese fleet's 5 fleet and 4 light carriers. The Americans were superior in every other category of ship except heavy cruisers. The Americans had an overwhelming advantage in carrier aircraft, with 891 embarked, compared with 430 aircraft embarked on the Japanese carriers. However, the Japanese aircraft had a considerable range advantage, being able to scout to 560 miles (1040 km) versus 350 miles (650 km) for the Americans and to attack at 300 miles (560 km) versus 200 miles (370 km) for the Americans. In addition, Ozawa would be sailing into the wind and thus could conduct flight operations while closing with the Americans. Ozawa planned to launch his carrier aircraft from outside the range of American counterstrikes and have them refuel and rearm at Guam, effectively doubling their strike value. However, this came at the cost of increasing pilot fatigue during the long flight to their targets.

But the advantage Ozawa counted most heavily on was the proximity of Japanese airfields, particularly at Guam, Rota, and Yap. As noted above, Ozawa believed he could count on the support some 500 land-based aircraft, which would have given him a slight numerical advantage over the Americans. It was here that the Japanese plan first began to break down. By the eve of battle on 18 June, Kakuta's land-based aircraft had accomplished next to nothing while suffering heavy casualties and damage to their bases.

The Japanese were beginning to equip their air groups with more modern light bombers, such as the D4Y "Judy" dive bomber and the B6N "Jill" torpedo bomber. However, many of the carrier air groups still included significant numbers of the older D3A "Val" dive bombers, which were too slow to keep formation with the newer models.

The most important Japanese handicap proved to be the poor training of the Japanese aircrew. The American pilots who fought in the battle all had no less than two years' training and 300 hours' flying time. By contrast, the Japanese had never been able to properly rebuild their air groups following heavy losses in the Guadalcanal campaign. The pilots with Ozawa's best carrier division averaged just six month's training, while those with Carrier Division 3 averaged only three months and those with Carrier Division 2 just two months. Training was further hampered by the decision to shift the carrier fleet to Tawi Tawi in the months before the battle:  The base was located so close to the equator that there were no trade winds to enable the slower carriers to get enough headwind to launch the most modern carrier aircraft. The Japanese aviators were simply no match for the Americans.

The Search Phase. On receiving Redfin's report that Ozawa had sortied on 13 June, Spruance calculated that there was still time to raid the airfields on Iwo Jima and Chichi Jima, knocking out the air bridge from Japan to Guam. The strikes were conducted by Task Groups 58.1 (Clark) and 58.4 (Harrill), which headed north on 14 June, launched strikes on the afternoon of 15 June and morning of 16 June, and was back with Spruance's main force by 18 June. The strikes destroyed at least 68 Japanese aircraft at the cost of 4 American aircraft. A number of small Japanese freighters were also wrecked.

Ozawa's force was again sighted late on 15 June by submarine Flying Fish, patrolling near San Bernardino Strait in the Philippines. An hour later Seahorse sighted Ugaki's battleship force coming north to join Ozawa. Spruance recalled Task Groups 58.1 and 58.4 and began assembling his carrier forces west of the Marianas. The landings on Guam, scheduled for 16 June, were postponed.

Cavalla sighted a Japanese oiler group just before dawn on 17 June. The American submarine unsuccessfully attempted to follow the group but later in the day found herself directly in the path of the main Japanese carrier group. This sighting report reached Spruance early in the morning of 18 June. Mitscher, Spruance's carrier commander, suggested racing west for a night engagement that evening, but Lee, commanding the battleships, strongly urged against seeking a night engagement due to lack of recent training in night tactics. Spruance also made the controversial decision to remain close to the amphibious forces off Saipan rather than sail towards the oncoming Japanese to close the range. His decision was influenced by intelligence obtained from Filipino guerrillas, who had captured Japanese plans that discussed the possibility of an end-run by Japanese surface forces after the main American fleet had been lured away by Japanese carrier forces. This was, in fact, the strategy that would later be employed by the Japanese at Leyte Gulf.

American reconnaissance aircraft just missed spotting Ozawa on 18 June. Ozawa inexplicably got no reconnaissance reports whatsoever from Japanese land-based air forces. However, Ozawa's own scout planes sighted the American force late on 18 June. One of Ozawa's carrier division commanders, Obayashi (CarDiv3), promptly began launching a strike against the Americans, but this was recalled just a few minutes later when Obayashi received Ozawa's battle plans. This may have been a missed opportunity for the Japanese, as Mitscher was unaware any Japanese carriers were within strike range and might have been caught by surprise at dusk.

Further reports came in to Spruance on the night of 18/19 June. By this time his carrier groups were arranged in a line from north to south, allowing each to conduct flight operations without interfering with one another, and the battle line had been formed to their west. A little before midnight, Spruance received an accurate position report for the Japanese via HF/DF that put them 300 miles (560 km) west-southwest of the Americans. Mitscher wanted to head west to strike at dawn, but Spruance was still worried about a Japanese end run and, after discussing the matter with his staff for an hour, refused. Spruance' caution was further reinforced by a report that submarine Stingray, located 175 miles (320 km) east-southeast of the HF/DF detection, had sent a garbled and unreadable transmission that Hawaii evaluated as having been jammed by the Japanese. Spruance believed that this was a contact report of a much closer Japanese attempting the very end run he feared, with the HF/DF detection possibly being a deception. Spruance kept the fleet on its eastward course:

We were at the start of a very large and important amphibious operation and we could not gamble and place it in jeopardy. The way Togo waited at Tsushima for the Russian Fleet to come to him has always been in my mind. We had somewhat the same basic situation.

The situation might have been clarified if Spruance had received a timely report from a radar-equipped PBM out of Saipan which, at 0115 on 19 June, detected over 40 ships some 75 miles (140 km) northeast of the HF/DF detection. But, for reasons that have never been adequately explained, the report did not reach Spruance until after 0800. Spruance knew the approximate number of ships available to Ozawa, and this report would have accounted for almost all of them, ruling out a Japanese end run in any force. But, as it was, a night search by radar-equipped TBFs in the early hours of 19 June turned back just 40 miles (75 km) east of Ozawa's leading elements. In the meanwhile, Japanese snoopers had confirmed the approximate position of the American fleet.

"The Great Marianas Turkey Shoot." Kakuta had had little success building up air strength in the Marianas, in part due to poor weather over the staging bases and in part due to the earlier American strikes against the Bonins and Iwo Jima. On the morning of 19 June, Japanese air strength at Guam numbered just 50 aircraft out of the 500 that had been promised. Nevertheless, beginning at 0530, the American fighter cover began intercepting land-based aircraft.  For the next four and a half hours, the American fleet vectored Hellcats against Japanese aircraft over Guam, destroying 30 fighters and 5 bombers.

Ozawa had formed up his fleet at 0400, with the three light carriers of Carrier Division 3 and most of his heavy surface units in the van, and the remaining five fleet and one light carriers of Carrier Division 1 and Carrier Division 2 about 100 nautical miles (185 km) to the rear. The van formation carried most of Ozawa's search seaplanes and, with its heavy antiaircraft screen, was meant to absorb any American counterattack. However, this left the antisubmarine screen for the rear group dangerously weak. Ozawa planned to launch his strikes from over 300 miles (560 km) out, where his ships would be out of range of any American counterattack. 

Ozawa launched his first search group, 16 Jake seaplanes from the van battleships and cruisers, at 0445. One of these sighted part of the American fleet at 0730. A second search group of a Jake and 13 Kates was launched at 0515 and lost half its number to the American fighter patrol without sighting anything but a few destroyers. Another group consisting of 11 Judys and two seaplanes from Mogami was launched at 0530.

The first Japanese strike (Raid I), consisting 16 Zero fighters, 45 Zero fighter-bombers, and 8 Jills, was launched at 0830 by Carrier Division 3. These were detected by American radar at 1000 at a distance of over 150 miles (280 km). Mitscher promptly recalled the fighters over Guam and, at 1019, gave the order to launch all available fighters from his carriers. All carrier groups turned into the wind and commenced launching at 1023, with the Japanese 75 miles (140 km) away. The Japanese strike paused to regroup at about this time, giving the Americans time to stack their fighters at a suitable altitude for interception and to fly off all bombers on their flight decks. Raid I was intercepted by over 30 fighters and lost 42 aircraft to the Hellcats and the American antiaircraft fire, at a cost to the Americans of a single fighter and a bomb hit on South Dakota that killed 27 men but did negligible structural damage.

The second Japanese strike (Raid II) was the largest of the day. It was launched from Carrier Division 1 and Carrier Division 2 at 0856 and was composed of 53 Judys, 27 Jills, and 48 Zeros. Raid II made the mistake of flying over the Japanese van group and lost two aircraft to friendly fire from the nervous gunners. Another eight were damaged and forced to return to their carriers. Raid II was detected by American radar at 1107 at a distance of 115 miles  (210 km) was intercepted at 60 miles (110 km) by the Hellcats, which shot down about 70 Japanese aircraft. The surviving Japanese wasted much of their firepower on unsuccessful attacks on picket destroyer Stockham, then attacked Lee's battle line. One Jill struck Indiana at the waterline, but its torpedo failed to explode. A small group of Judys broke through to Montgomery's task group and scored some very near misses on Wasp and Bunker Hill. The Japanese lost a total of 97 aircraft from Raid II.

Raid III was launched at 1000 from Carrier Division 2 and consisted of 15 Zero fighters, 25 Zero fighter-bombers, and 7 Jills. This group was diverted too far north by a garbled report from the third reconnaissance group. Most returned to their carriers, but about 20 received a corrected sighting report and turned south, avoiding Lee's battle line and attack Clark's task group. They were detected 99 miles (180 km) out and intercepted at 1300 at a distance of 50 miles (90 km) by 40 Hellcats. Seven Japanese aircraft were lost.

At this point there was a brief lull in the battle, during which Mitscher sent out a search mission. It failed to find the Japanese fleet.

Raid IV was launched at 1100 from Carrier Division 1 and Carrier Division 2. It consisted of 30 Zero fighters, 9 Judys, 27 Vals, 10 Zero fighter-bombers, and 6 Jills. These were also mislead by the garbled sighting report from the third reconnaissance group and found no targets at first. One group headed for Rota. On the way, they ran across Montgomery's task group but were unable to score any hits. A somewhat larger group headed for Guam. These aircraft had already jettisoned their ordnance in preparation for landing when they were intercepted by 27 Hellcats from Cowpens, Essex, and Hornet. Many of the Japanese planes had lowered their landing gear and were sitting ducks. The Hellcats destroyed 30 out of the 49 aircraft, and the remaining 19 landed in such a damaged state that they were judged beyond repair. A total of 73 aircraft out of the 82 in Raid IV were destroyed or damaged beyond repair.

The swarms of Hellcats that intercepted the four Japanese strikes were expertly directed to their targets from the Combat Information Centers (CICs) of the American carriers. Weather conditions were perfect for the Americans, with clear skies, unlimited visibility, and the right humidity to form vapor trails. Those Japanese aircraft that got through the American fighter umbrella faced the lethal U.S. 5"/38 dual-purpose guns of the American battleships and carriers. Damage to the American fleet was minimal, and about 315 Japanese aircraft were lost in the air, on the ground, or on sunken carriers, against a loss to the Americans of just 27 aircraft. This phase of the battle was so one-sided that it became known as "The Great Marianas Turkey Shoot."

While the Hellcats were slaughtering the Japanese carrier strikes, Spruance had ordered his own strikes against Guam. At 1040 Hornet launched a force of 17 Helldivers and 7 Avengers escorted by 12 Hellcats to bomb Orote Field. The field was struck again at 1300 by a group of SBDs that had been circling for two hours after being launched from Lexington to clear its flight deck. Other American bombers launched under similar circumstances continued to attack throughout the day.  Orote was essentially shut down, and many of the aircraft from Raid IV that had to be written off after landing had crashed on the bombed-out runway. But this came at a heavy cost: Antiaircraft fire over Orote was reportedly the worst yet encountered in the Pacific War, and the Americans lost seven aircraft over the airfield.

Submarine Actions. Just after Raid II was launched, the brand-new Taiho was hit by a single torpedo from Albacore, which had been forced to fire by "seaman's eye" after her fire control computer was fed incorrect data. A second torpedo was sighted by Warrant Officer Komatsu Sakio, who sacrificed himself to crash-dive on the torpedo. Albacore was then subjected to a halfhearted depth charging and got clean away. Taiho ought to have survived a single torpedo hit, but a gasoline tank had been fractured, leaking gasoline into the well of the jammed forward elevator. Inept damage control led to a fatal gasoline vapor explosion at 1532 that tore the carrier apart. Only about 500 of the crew of 2150 were saved. The survivors included Ozawa and his staff, who transferred to heavy cruiser Haguro to continue directing the battle.

At 1152 Cavalla raised periscope to find herself close to a large Japanese carrier. This was the  veteran Shokaku, which was maneuvering to recover aircraft. By 1220 Cavalla was in firing position and let loose with six torpedoes, the last two fired on the way down as a Japanese destroyer was rapidly closing in. Shokaku was fatally struck by four torpedoes, sinking shortly after 1500. Cavalla was subjected to a brutal depth charging, dodging 106 depth charges over the next three hours, but she also got away.

American Counterattack. Spruance was finally convinced that a Japanese end run was highly unlikely, and at 1500 on June 19 he gave Mitscher, permission to pursue Ozawa's fleet. Mitscher left Harrill's group, which was low on fuel, to continue interdicting the airfields on Guam and Rota, and he pursued the Japanese with this remaining three carrier groups. Because these were recovering aircraft, they were unable to head west until 2000, and Mitscher dared not steam faster than 23 knots in order to conserve fuel. However, Ozawa was unaware of the extent of his aircraft losses on 19 June, believing that most of his aircraft had landed safely on Guam, and he was slow to disengage. As a result, the Japanese fleet was finally located by American search planes at 1540 on 20 June.

Though the enemy was at extreme range and it was late in the day, the aggressive Mitscher launched a strike of 85 fighters, 77 dive bombers, and 54 torpedo bombers. The strike reached the Japanese just as the sun was setting, but inflicted only modest damage, sinking carrier Hiyo and oilers Genyo and Seiyo Maru and damaging carriers Zuikaku,  Junyo, and Chiyoda and battleship Haruna. Ozawa got about 75 planes into the air, which intercepted the Americans very close to the Japanese ships and shot down a number. Other ran out of fuel on the long flight back to their carriers, and over eighty aircraft failed to make it back, though Mitscher accepted the risk of turning on the carrier's running lights, deck lights, and searchlights to guide them in after dark. All but 49 of the aircrew were eventually rescued.

It was not just the Americans who suffered from night landings. Ozawa's fighters did not begin landing until 1930 on 20 June, and many ditched or cracked up on damaged flight decks. Ozawa found that he had just 35 operational aircraft left. His halfhearted attempt to seek a surface engagement, ordered at 1900, was canceled at 2205. Toyoda had already ordered him to retire. None of Ozawa's remaining ships had suffered damage to their machinery and Ozawa was able to maintain a speed of 20 knots, ensuring his escape. Spruance nevertheless pursued until late on 21 June in hopes of catching any cripples. There were none, and Spruance called off the chase, ending the battle, at 2030.

In spite of missed opportunities, the battle was a decisive American victory. Total Japanese air casualties were about 476 aircraft and 445 aviators, versus 130 aircraft and 76 aviators for the Americans. The Japanese carriers returning from the battle had only 35 aircraft left between them. The loss of Japanese carrier aircrew was so great that the battle spelled the effective end of Japanese carrier power.

American order of battle, 29 June 1944:

Japanese order of battle, 29 June 1944:

References

Dull (1978)
Morison (1953)

Tillman (2005)

Werneth (2008)

The Pacific War Online Encyclopedia © 2006, 2009, 2012 by Kent G. Budge. Index

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