In August 1945, Imperial Japan surrendered to the Allied Powers. From September 1945 to April 1952, the United States occupied the defeated country. Douglas MacArthur, an American army general and the Supreme Commander for the Allied Powers (SCAP), attempted to transform Japanese society from an authoritarian regime into a budding democracy. Japan's new constitution, written in English in one week by MacArthur's General Headquarters (GHQ) in Tokyo, guaranteed every citizen freedom of expression and academic freedom. The notorious "Red Purge" was instituted nationwide in the final phase of the occupation, from July 1947 to March 1951, and proved to be a critical test for the survival of academic freedom. The GHQ ordered the Japanese Cabinet to fire communists and their sympathizers from private companies, government offices, and all educational institutions. American educator Dr. Walter C. Eells, who served at GHQ as adviser on higher education, became a central figure in the "Red Purge" of Japan's educational system, and thus emerged as one of the most infamous figures of the U.S. occupation. Between July 1949 and May 1950, GHQ's Civil Information and Education Section (CIE) dispatched Eells to thirty national universities to call for the immediate dismissal of communist professors. Often the Eells case is interpreted solely from the Japanese perspective. But this article aims to reveal the complex internal tensions and discussions within the CIE and, in particular, elaborates Eells's own view. An awareness of these hidden but critical factors offers a more refined understanding of the "Eells typhoon ("Iruzu senpu")," as the Japanese called it at the time. In order to place the Red Purge in Japan in a broader context, the author presents an overview of anticommunist sentiment in the United States. (Contains 100 footnotes.)