The Marianas archipelago extends 500 miles from north to south. American planners focused on the larger islands which were heavily fortified by the Japanese. First targeted was Saipan, the largest island of the northern Msrianas with the largest Japanese garrison. It was 15 miles long and 7 wide thus parmitting combined arms maneuvers. Inland hill masses overlooked sandy beaches and provuided cover for an extended defense. The taking of the Marianas required separate invasions for each of the islands to be seized. Saipan, Tinian and Rota are the principal islands of the Northen Marianas.The large Japanese garrisoms on Saipan and Guam meant that major invasions had to be mounted. Tinian was less of a problem. The naval planners decuided to simply cutt off Rota rather than invade it. The Marianas were different than the other islands of the Central Pacific campaign in that there were a substantial civilian population. And on Saipan this included Japanese civilians. When the Japanese first arrived, there were only about 4,000 Chamorros in the Northern Marianas, but a larger poplation on Guam. The Japanese brought in Japanese and immigrant workers who numbered about 45,000 at the time of the War. They dwarfed the indigenous population and overwhelmed the native culture. The Marianas proved to be one of the bloodiest battlegrounds of the Pacific War. There location closer to the Home Islands than the rest of Micronesia, the Japanese tenaciously defended them as essential to maintaining a defensive perimeter. The United States mounted a massive invasion of first Saipan and then Guam. The outgunned Japanese garisons fought to the death.
The Marianas showed dramatically how flawed the Japanese strategic conceot was. Japanese strategists before the War discussed the huge numbers of Pacific Islands and thought that the American fleet could not possiblly penetrate the Pacific island barrier. [Matsuo] This had some merit as long as Japan possessed the dominant naval force that could support and protect the island garisons. And given the industrial power of the United States, this was unlikely. And this proved to be the case. After losing naval dominance, the Pcific island garisons were not only vulnerable to Americam attack, but Japan had great difficulty supporting them. As a result, in the Marianas, the battle that would decide the fate of the Japanese Empire would be fought by 31,000 men on Saipan. Japan with a hige army mostly deployed in China had no way of supporing the doomed Saipan garison. Even the nbearby Rota and Guam garisoins could not offer support. And when the Imperial Fleet attempted to intervene, the fleet air arm was destroyed. Spreading troops out accross a huge number of Pacific Islands simply allowed the United States to isolate the garisons and defeat the ones occupying islands deemed important in detail. The Japanese most elemetary military principle is to win battles by concentrating forces at strategic points. The Japanese island barriers led Japan to 1)difuse its forces and 2) at locations where they could not be supported. And of course it would be from the Marinas that the B-29s dropping the two atomic bombs would reach Japan.
There were four principal Marianas Islands. Each of them would serve as air bases from which the United States could commence the strastegic bombing of the Home Islands. American Marines in 1943 demonstrated that even heavily foortfied garrisons could not repel invasions without air and naval support. Thus the Imperial Fleet intervened for the first time since the Solomons (1942). America carrier strikes destroyed the aircraft on the islands before a Japane carrier force arrived to repel the invasion. The American carrier aurcraf not only repelled the Japsne fleet, but decimated the attacking plnrs. After this, each island could be invaded in separate opeations. The isolated garisons had no way of supporting each other and after the Japanese carriers were defeated, had no hope of support or supply deliveries. Each if the four islands were different. Not only was tge terraine different, but for the first time the United States encountered Japanese civilians, especially on Saipan. Saipan and Tinian were close together. Guam was a former American possession, far to the south. Admiral Nimitz decided to forego an invasion of Rota as the other islands provided adequate sites for the needed airfields. The Japanese garrison there was left to languish.
Kinoaki Matsuo. The Three Power Alliance And The United States Japanese War. Matsuo's book explained how Japan could win a Pacific war with the United States. He was an intelligence officer who served as a liaison between the Japanese Foreign Office and the Admiralty. He argued that the "... the United States will be obliged to exercise prudence and self-restraint toward Japan at least until 1945." He believed that it would take this long for America to build up amidabe military force.
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