The Marianas Campaign began with the invasion of Saipan on June 15, 1944, following several days of shore bombardment and aerial attacks. These preliminary attacks alerted the Japanese to American intentions and Admiral Toyoda sent the last available carrier force, the Mobile Fleet, to repel Admiral Spruance’s Fifth Fleet from the Mariana Islands. Wary of such an attack, the American fleet detected and engaged the incoming planes before they reached their targets. The Battle of the Philippine Sea proved to be the last of the great carrier battles of the war, and it blunted the offensive capabilities of the Imperial Japanese Navy.
The Japanese Mobile Fleet was commanded by Vice-Admiral Ozawa Jisaburo. This force was built around nine aircraft carriers. Typically, these carriers are classified as fleet carriers and light carriers, reflecting principally the number of aircraft they could carry, but also the size of these vessels and the number of anti-aircraft guns with which they were furnished.
The fleet carriers consisted of the Taiho, which was Ozawa’s flagship, the sister ships Shokaku and Zuikaku, which were nearly as powerful and two lesser carriers, the Hiyo and Junyo. The Taiho, which had only become operational in March, had been built with the lessons of Midway in mind. Portions of the air deck had been armored and it employed updated anti-aircraft defenses, with six pairs of 100 mm guns and fifteen emplacements of triple 25 mm guns. It carried 75 aircraft of various types, although in theory it could carry as many as 84. The veteran Shokaku and Zuikaku carried 72 aircraft each, while their anti-aircraft defenses consisted of eight paired 127 mm guns and twelve emplacements of triple 25 mm guns. The Junyo and Hiyo, also sister ships, were repurposed passenger ships that carried 53 aircraft each; their more modest anti-aircraft provisions included twelve 127 mm guns and 24 single emplacements of 25 mm guns.
The Zuiho, Ryujo, Chiyoda and Chitose completed the roster of carriers. As light carriers, their capacity was roughly half of that fielded by the larger carriers. The Ryujo carried 36 aircraft, for example, while the Zuiho only had thirty. Their anti-aircraft capabilities were also less, with the former mounting sixteen pairs of guns and the latter mounting only eight pairs. Smaller and weaker than the fleet carriers, they still contributed a substantial portion of the total of 473 planes dispatched in the attack. While this was much less than the numbers fielded by fifteen American aircraft carriers, the Japanese intended to gain an advantage by operating from a distance beyond the operational range of American carrier-based aircraft. Japanese planes had a longer range and this was meant to be enhanced by landing on Saipan for refueling. Had this plan worked, the ability to fight on the return trip could have acted as a force multiplier for the Japanese.
In the context of a carrier battle, all other vessels, even the great battleships, can be considered support vessels. These included five battleships, thirteen cruisers and twenty-eight destroyers.
Task Force 58, the fighting core of the U.S. fleet, was organized as a Fast Carrier Task Force, consisting of fifteen carriers along with their support vessels. Generally, they were divided into four task groups, each with four carriers (one made do with only three), but in this case, six battleships were drawn from their respective groups and became the nucleus of a fifth task group. Admiral Spruance was present in the task force but, during the engagement, command was exercised by Vice-Admiral Marc Mitscher.
Seven of the carriers were fleet carriers (designated C.V. in the U.S. Navy), with the Yorktown class and the Essex class both represented by such vessels as the USS Enterprise and the USS Bunker Hill, respectively. Carrying capacities varied, often including 80 planes or more. By 1945, vessels of the Essex class were capable of carrying as many as 119 planes. Anti-aircraft armament varied from vessel to vessel and were upgraded over time, but carriers from the newer Essex class had been built with as many as 67 emplacements, of which twelve were 127 mm guns, eleven mounted four 40 mm guns and 44 were 20 mm guns.
The other eight carriers were light carriers (C.V.L.). The Independence class of light carriers had been created by converting light cruisers into aircraft carriers during their assembly. Carrying capacity was low, amounting to only 33 aircraft. In contrast, the Sangamon class of escort carriers (C.V.E.) could carry 45. Escort carriers were slow, however, while light carriers could maintain the speeds required in the Fast Carrier Task Forces. Taken together, the American carriers had more than 900 aircraft, of which 450 were fighters. In the first phase of the battle, when the Americans were on the defensive, it was these fighters that were crucial.
Support vessels included seven battleships, although six of these were assembled in the impromptu fifth task group set a few miles forward of the center of the American line. Twenty cruisers and 67 destroyers filled out each of the five task groups, forming a circle out of each. Crucially, the American forces employed a forward defense of submarines, including the U.S.S. Albacore and the U.S.S. Cavalla.
The American fleet came out of the battle largely unscathed, with 130 airplanes lost and minimal damage to the fleet itself. The Japanese, however, lost three prized warships; the submarines Albacore and Cavalla sank the Taiho and Shokaku, respectively, while carrier-based aircraft sank the Hiyo, along with two oil tankers. The same air attack dealt substantial damage to two more carriers, the Zuikaku and Chiyoda, as well as one battleship (Haruna) and a heavy cruiser (Maya). In the long run, it was the near total loss of the Japanese aircraft and of their experienced pilots that decided the battle. The Japanese were able to save seven aircraft carriers, but with only 35 functional planes among them, they ceased to have any military significance.
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