From June 4 to 7, 1942, the U.S. Navy ambushed and then devastated a Japanese strike force near Midway Island … On June 7, six months to the day after Pearl Harbor, a front-page report in the Chicago Tribune hinted at the astonishing secret that enabled the American victory … Savvy readers knew that the dozen paragraphs of intricate details had to mean Washington had cracked Japan’s secret naval code … Opening this testimony [now] could explain how Johnston learned one of this nation’s most valuable secrets, how perilous the Navy thought the leak was, and why the investigation halted; the filing alludes to the possibility that the Navy didn’t want to tell grand jurors about its codebreaking coup.

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