The Hypo “Dungeon”
U.S. cryptographers at Hawaii’s station Hypo (the British military designation for “H” for the Heeia radio post) had managed to decipher much of the Japanese Navy’s most important code, dubbed JN-25. Working in a windowless basement they called “the dungeon,” the codebreakers under the direction of the brilliant Commander Joseph Rochefort, noticed increased Japanese radio traffic referencing a point called “AF.” It was becoming clear that “AF” was the focal point of a major upcoming operation featuring a carrier group and at least one surface fleet, and it would be executed either on June 4 or 5.
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