Battle of the Philippine Sea

• 1. The Recovered Z Plan

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  On the 31st of March 1944, Admiral Mineichi Koga died when his Kawanishi H8K aircraft crashed into a typhoon. His chief of staff, Vice Admiral Shigeru Fukudome, was flying in an accompanying plane and also crashed. Fukudome survived the crash, but the briefcase containing the Z Plan documents did not sink with the destroyed aircraft. Filipino guerillas recovered the documents over the next few weeks and transported them to General Douglas MacArthur's Military Intelligence Service in Brisbane, Australia. MIS forwarded the translated Z Plan to Admiral Chester Nimitz in Honolulu. The Japanese plans were quickly dispatched to fleet commanders in the Philippine Sea by June. A new commander-in-chief of the Combined Fleet, Admiral Soemu Toyoda, finalized the plans known as Operation A-Go. This plan did not change much from the original Z Plan. By early June 1944, the U.S. Navy knew exactly what the Japanese intended to do during the upcoming naval battle.

• 2. Aerial Slaughter Over Saipan

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  At 05:50 on the 19th of June 1944, a Mitsubishi A6M Zero found Task Force 58. After radioing his sighting of U.S. ships, the bomb-carrying Zero attacked picket destroyer USS Samuel B. Roberts but was shot down by the destroyer USS Nicholas. Alerted, the Japanese began launching their Guam-based aircraft for an attack. These were spotted on radar by U.S. ships. A group of thirty Grumman F6F Hellcats were dispatched from USS Lexington to deal with the threat. Minutes later, additional radar contacts were seen, which were later discovered to be the additional forces being sent north from other islands. A battle broke out in which 35 Japanese aircraft were shot down for the loss of a single Hellcat. At 10:23, Mitscher ordered TF 58 to turn into the wind on course east-southeast and ordered all fighter aircraft aloft. He then sent his bomber aircraft aloft to orbit open waters to the east rather than leaving them in a hangar deck full of aircraft vulnerable to a Japanese bomb attack. By the end of the first day, Japanese losses exceeded 350 planes while about 30 American planes were lost.

• 3. Submarines Sink Giants

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  At 08:16 on the 19th of June 1944, the submarine USS Albacore sighted Ozawa's carrier group. Lieutenant Commander James W. Blanchard selected the closest carrier as his target, which happened to be Taihō, the largest and newest carrier in the Japanese fleet. As Albacore was about to fire, her fire-control computer failed, and the torpedoes had to be fired by eye. Determined to go ahead with the attack, Blanchard ordered all six torpedoes to be fired in a single spread. Of the six torpedoes fired, four veered off-target. The sixth torpedo struck the carrier on her starboard side and ruptured two aviation fuel tanks. Meanwhile, another submarine, USS Cavalla, maneuvered to an attack position on the 25,675-ton carrier Shōkaku by about noon. The submarine fired a spread of six torpedoes, three of which struck Shōkaku on her starboard side. Badly damaged, the carrier came to a halt. One torpedo had hit the forward aviation fuel tanks near the main hangar, and aircraft that had just landed and were being refueled exploded into flames. With her bows subsiding into the sea and fires out of control, the captain gave orders to abandon ship. Within minutes, there was a catastrophic explosion of aviation fuel vapor which had built up between decks, which blew the ship apart.

• 4. Spruance's Cautious Gamble

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  Shortly before midnight on the 18th of June, Nimitz radioed Spruance that a Japanese vessel had broken radio silence. Mitscher considered whether the radio messages were a Japanese deception. Arleigh Burke, Mitscher's chief of staff, assumed that battle line commander Willis Lee would welcome the opportunity for a night surface encounter. But Lee strongly opposed such an encounter. Having personally experienced a confused night action off Guadalcanal, Lee was not enthusiastic about a night engagement with Japanese surface forces. Shortly after learning Lee's opinion, Mitscher requested permission from Spruance to move TF 58 west during the night. Spruance considered for an hour, then refused Mitscher's request. Mitscher's staff was disappointed with Spruance's decision. Burke later commented: We knew we were going to have hell slugged out of us in the morning. We knew we couldn't reach them. We knew they could reach us. Spruance's decision was influenced by his orders from Nimitz, who had made it clear that the protection of the invasion fleet was the primary mission of TF 58. Spruance had concerns that the Japanese would attempt to draw his main fleet away from the Marianas with a diversionary force while slipping an attack force in to destroy the landing fleet.

• 5. Fuel and Training Deficits

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  Japan no longer had enough oil tankers to transport the required volume of petroleum from the Dutch East Indies to Japanese refineries. Without adequate supplies of refined residual fuel oil, Japanese aircraft carriers refueled with unrefined Tarakan petroleum in June 1944. This undesalted petroleum damaged boiler tubes, and the unremoved naphtha fraction volatilized the fuel to form explosive atmospheres incompatible with aircraft carrier damage control procedures. The American F6F Hellcat fighter proved its worth, as its powerful engine generated superior speed, while its heavier armor and firepower made it rugged and deadly. The Japanese on the other hand were still flying the A6M Zero which, though highly maneuverable and revolutionary during the early stages of the Pacific War, was now underpowered, fragile and essentially obsolete by 1944. In addition, the D4Y Judy, though fast, was also fragile and easily set on fire. Japanese naval airmen were inadequately trained. The Japanese training programs could not replace the quality aviators lost during the past two years of the Pacific Campaign. Flying against the well-trained and often veteran U.S. aviators, it was a one-sided contest.

• 6. The End of Carrier Dominance

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  That night, Toyoda ordered Ozawa to withdraw from the Philippine Sea. U.S. forces gave chase, but the battle was over. The four Japanese air strikes involved 373 carrier aircraft, of which 243 were lost and 130 returned to the carriers. After the second day of the battle, losses totaled three carriers, more than 350 carrier aircraft, and around 200 land-based aircraft. In the five major carrier-on-carrier battles, from the Battle of the Coral Sea to the Battle of the Philippine Sea, the IJN had lost nine carriers, while the USN had lost three. The aircraft and trained pilots lost at Philippine Sea were an irreplaceable blow to the already outnumbered Japanese fleet air arm. The Japanese had spent the better part of a year reconstituting their depleted carrier air groups, and the American Fast Carrier Task Force had destroyed 90% of it in two days. The Japanese had only enough pilots left to form the air group for one of their light carriers. As a consequence, during the Battle of Leyte Gulf four months later, they sent out a decoy carrier group with only 108 aircraft across six carriers that was sacrificed in an attempt to draw the American fleet away.