Why did the Japanese take over the Pearl Harbor?

Answer 1

The Japanese goal in attacking Pearl Harbor was to do enough damage to the US Fleet that the US could not interfere with the main Japanese plan. The main plan was the "southern operation". This was the conquest of the Dutch East Indies (today's Indonesia) for the abundant oil there, and British Malaya (now Malaysia) for the rubber, and other parts of southeast Asia, for the natural resources they needed to feed their war machine.

The Japanese believed the US would go to war with Japan over this wave of invasions. The Philippine Islands were a US possession at the time, and the US had a major air base and navy base there. The Japanese planned to conquer the Philippines at the same time as they were attacking all their other targets, to neutralize US forces there and prevent US interference. The Japanese were divided over whether to also attack the US Fleet in Hawaii. They were already going to be spread pretty thin, and an attack on Hawaii would divert the main striking power of the Japanese Navy from supporting the southern operation. Admiral Yamamoto though believed the only chance for victory the Japanese had was to paralyze the Americans with a powerful strike that would buy the Japanese six months time to complete their conquests. This was just about exactly what he got from the Pearl Harbor attack. The Japanese hoped that when the Americans saw what the Japanese had done, the Americans would just give up and let them keep their conquests.

Some of the more aggressive younger officers involved in planning the attack wanted to land troops in Hawaii and conquer these islands as well. This would deny the use of the islands as a base for any American counter offensives. But this was never part of the plan. The Japanese already had enough to do with four simultaneous invasions plus the attack on Pearl Harbor.

Since the Japanese goal was only to damage the US Fleet, they ignored some very high value targets, damage to which might have helped them quite a bit as the war went on. Specifically, they did not target at all the fuel farm at Pearl Harbor, the drydock, or the submarine base. If they had seriously damaged the drydock repair of battle damaged US ships would have to be done 2200 miles farther east, on America's west coast. If they had destroyed the fuel farm it would have been impossible for the fleet to continue being based in Pearl Harbor, and the entire US Pacific Fleet would have had to withdraw to and operate from the west coast. During the war US submarine sailors amounted to 1% of the US Navy, but they sank 55% of Japanese ships sunk. Damage to the machine and repair shops at the submarine base within Pearl Harbor would have very seriously hampered this effort. But the Japanese ignored all these targets and concentrated on warships.

Answer 2

"The attack was intended as a preventive action in order to keep the U.S. Pacific Fleet from interfering with military actions the Empire of Japan was planning in Southeast Asia against overseas territories of the United Kingdom, the Netherlands, and the United States."