I'm not entirely sure on info you wanted but reason why:
From Wiki:
It had always been the intention of the American planners to bypass the Carolines and Palaus and to seize the Marianas and Taiwan. From these latter bases communications between the Japanese homeland and Japanese forces to the south and west could be cut. In addition, from the Marianas Japan would be well within the range of an air offensive relying on the new B-29 Superfortress long-range bomber with its operational radius of 1,500 mi (2,400 km).
Saipan, one of the 15 chain islands of the Mariana, was only approximately 1,300 mi (1,100 nmi; 2,100 km) away from home islands of Japan. It was a very important strategic point for the U.S. during the Second World War in the Pacific Theater. It was the key position for the Americans to bring the war to Japanese homeland.[19]
After the battle, Saipan became an important base for further operations in the Marianas, and then for the invasion of the Philippines in October 1944. Bombers based at Saipan attacked the Philippines, the Ryukyu Islands and Japan. In response, Japanese aircraft attacked Saipan and Tinian on several occasions between November 1944 and January 1945. But the US invasion and capture of Iwo Jima put an end to those Japanese air attacks. With the position secured, American army could also make advancement in the Philippines and also make direct contact with its Chinese ally.
For the Japanese, the defeat in the battle made the futility of the War in the Pacific all the more apparent. According to one Japanese admiral: "Our war was lost with the loss of Saipan." The famous American Marine Corps General Holland Smith said "it was the decisive battle of the Pacific offensive" and "it opened the way to the Japanese home islands."[20] Four months later, the 100 B-29 bombers that took off from Saipan and attacked Tokyo, showed the decision to take Saipan was correct.
The loss of Saipan was a heavy blow to the Japanese ambition. A meeting of senior generals and admirals decided that a symbolic change of leadership should be made and Prime Minister Hideki Tōjō should step aside. In addition, the Emperor should move away from day-to-day affairs so as to avoid looking too directly involved with the now losing war, to distance himself from blame if the war were lost. "shogun" Tōjō.[2][unreliable source?] Tōjō agreed and submitted his resignation. Emperor Hirohito—considering Tōjō the strongest war leader Japan had—resisted. Tōjō considered trying to shuffle the Cabinet but encountered too much hostility and gave up.[2][unreliable source?] On 18 July, Tōjō submitted again his resignation, this time unequivocally. His entire cabinet resigned with him.[21]
During the course of the battle, Japanese accounts for the home front had concentrated on the fighting spirit and the heavy American casualties, but familiarity with geography would demonstrate that the battles slowly progressed northwards as the American forces advanced, and the reports ceased with the final battle, which was not reported to the public.[22] After Tōjō's resignation, an accurate, almost day-by-day, account of the fall was published by the army and navy, including the nearly total loss of all Japanese soldiers and civilians on the island, and the use of "human bullets"; the report had devastating effects on Japan, with the mass suicides being taken not as evidence of the Imperial Way but of defeat.[23] This was the first time that the Japanese forces had accurately depicted a battle since Midway, which they had proclaimed a victory.[23]
as for planes used google "Battle of the Philippine Sea" and try to find US 5th Fleet OoB
HTH
Juha