U.S. intelligence intercepted a Japanese diplomatic cable instructing the Honolulu consulate to burn its codebooks and destroy sensitive documents, one of several signals in the days before Pearl Harbor suggesting an operation was imminent. Buried among a flood of other intercepted traffic and hampered by slow translation and interagency friction, the warning failed to trigger the alarm that might have changed the outcome four days later.
American codebreakers under the MAGIC program had been reading much of Japan's diplomatic traffic for months, and the instruction to destroy ciphers in Hawaii specifically—rather than at other consulates worldwide—should have stood out as an alarming anomaly. Instead, it arrived as one cable among hundreds, processed by an overstretched translation staff working through stacks of intercepts with no dedicated system for flagging urgency.
Historians have long debated how differently events might have unfolded had this and other fragments—including reports of unusual Japanese fleet movements and coded warnings from Australian and British intelligence—been assembled into a coherent picture in Washington and relayed urgently to commanders in Hawaii. Admiral Husband Kimmel and General Walter Short, the Pacific commanders at Pearl Harbor, later insisted they had never been given the full weight of the intelligence Washington possessed. The failure to connect these dots became a defining case study in the study of intelligence failure, cited for decades afterward in American discussions of every subsequent surprise attack, from Pearl Harbor's own memory to 9/11.