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Some have asked why Japan did not invade Hawaii when they attacked Pearl Harbor; they had us on the ropes and it's only logical that they would use the opportunity to take our main naval base in the Pacific Ocean. This view, however, does not take any of the background information and history of the conflict into account.
Japan did not invade Hawaii at the same time it attacked Pearl Harbor because it was counter to its goals at the time. The sole purpose of the attack was to keep the US Navy Fleet from threatening Japan's conquest of the Philippine islands, Dutch East Indies, and other resource-rich lands south of the Japanese homeland. Any conquest and holding of the Hawaiian islands would have drained strength from this primary goal; indeed Admiral Yamamoto had to fight to get all six carriers of the Kido Butai kept on the mission as some felt they would be better used supporting the invasion forces.
In the years prior to the war, the Japanese military was split into two factions that were constantly fighting for power and control; the Imperial Japanese Army and Navy. Each had their own goals and ideas of what would best further Japan. The Japanese Army was focused on the conquest of China, which had it's roots in a war between the two countries that had been fought just before the turn of the century. Following their aquisition of German-held territories at the end of the First World War, the Army had sought to expand the territory occupied and influence in China.By 1937, the incidents and skirmishes that had followed had created an all-out, but undeclared war. Incidents such as the assault on Nanking, later titled "The Rape of Nanking," created chinese civilian deaths in excess of 300,000 men, women, and children. In response to the escalating fighting and deaths, the countries such as Great Britain, the United States, and the Dutch East Indies put pressue on Japan to stop their acts and withdraw. Japan's refusal only heightened tensions, and
Navy Captain Kami Shigenori was asked to do a study for the Imperial Japanese Army at the end of December, 1941 on the logistical support necessary to support an occupation force on Hawaii. His report, completed by January 11 of 1942, indicated that it would take at least sixty transport loads a month (essentially two ships a day) to sustain the force and islands . While this was done after the initial attack, it does show the logistical drain this would have been on Japan's Army and Navy when they were trying to secure lands in the Philippines and Dutch East Indies.
To put this in a mathmatical perspective, if we were to plot a course on a straight line from Yokohama to Oahu, deviating only for land obstructions, we get a distance of nearly 4,000 miles. If we assign a generous cruising speed of 15 miles per hour, our ship will take just over 11 days to reach Hawaii from Yokohama. If we need two a day, we need 22 ships heading to Hawaii at any one time to sustain the force. But wait, once they get there, they need to come back, so in actuality we'll have 44 ships sailing to and from Hawaii at any point.
However, it also takes time to load and unload ships; let's give them four days at each port; that means we need an additional sixteen ships added to cover the down time (Two ships in each port for four days equals 16). So we really need sixty ships dedicated to the Hawaiian occupation just to sustain the forces. These are just transports; we're not factoring in the escort ships that would be needed to screen for American submarines, and overhead built into the system to compensate for any ships sank by American forces.For Further Reading:
"Rising Sun: " John Toland
"At Dawn We Slept"
"Shattered Sword: The Untold Story of the Battle of Midway"
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