Japan planned to invade and occupy Hawaii after the Pearl Harbor attack, but abandoned the idea after losing four key aircraft carriers in the Battle of Midway the next year, according to a professor who has studied World War II documents in Tokyo.

The plan called for disbanding Hawaii's large corporations, for replacing sugar and pineapple crops with taro and sweet potatoes, bringing in Japanese fishermen to build a fishing industry, sending second-generation Japanese-Americans through reeducation programs and reviving the Hawaiian monarchy as a puppet government, says Prof. John J. Stephan of the University of Hawaii.

A major proponent of the invasion was Adm. Isoroku Yamamoto, commander of Japan's fleet. He saw air power as the key to victory in the Pacific and foresaw that the United States would launch attacks on Japan from Hawaii-based carriers.

Shortly after the Pearl Harbor raid in December 1941, the invasion ideas was tabled as too difficult, Stephan says, but after Gen. James Doolittle's B25 hit Tokyo from the carrier Hornet in April 1942, the plan was revived and three Japanese army divisions were released for it.

But then in June came the Midway defeat.Military leaders gave up the invasion plan, as Japan was forced to divert most of its naval strength to defensive operations in the western Pacific and Southeast Asia. But because the Japanese population was not told of the Midway battle, civilian strategists continued to work out the details of the invasion plan.