Station HYPO Background
Station HYPO, also known as Fleet Radio Unit Pacific (FRUPAC) was the United States Navy signals monitoring and cryptographic intelligence unit in Hawaii during World War II. It was one of two major Allied signals intelligence units, called Fleet Radio Units in the Pacific theaters, along with FRUMEL in Melbourne, Australia. The station took its initial name from the phonetic code at the time for “H” for Heʻeia, Hawaii radio tower. The precise importance and role of HYPO has been the subject of considerable controversy, reflecting internal tensions amongst US Navy cryptographic stations.

HYPO was under the control of the OP-20-G Naval Intelligence section in Washington. It was located, prior to the attack on Pearl Harbor of December 7, 1941, and for some time afterwards, in the basement of the Old Administration Building at Pearl Harbor. Later on, a new building was constructed for the station, though it had been reorganized and renamed by then.

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