The Optics of MAGIC: FDR’s 1941 SIGINT Stumbles and Japan’s Hidden Plans for America (1940–1941)

Abstract

Abstract Since the 1941 Japanese attack against Pearl Harbor, numerous politicians, government analysts, and scholars have questioned how the Roosevelt administration could have been caught so unawares and incurred such heavy casualties at the onset of the Second World War. The postwar disclosure that President Franklin D. Roosevelt and his senior advisers had access to Japan’s diplomatic message system through a small joint Army–Navy cryptologic program, called MAGIC, further complicated the search for answers. Although many historians have cited the value of MAGIC linked to Pearl Harbor, few have looked at the overall intelligence value of Japan’s American targets for data collection beyond the first strike situation. Marshall’s ordered comprehensive review of the MAGIC cables in the days following the December 7 attack failed to explain the reason for a Japanese data dump of several hundred messages in length. What did military intelligence miss? What does Signals Intelligence show us about Japan’s post-Pearl Harbor plans for the United States? A deep read of the material contextualized by other intelligence reports reveals administrative optics likely blinded the American nation to Japan’s intended wartime game plan, setting up the potential for a disaster as great as the surprise attack on Pearl Harbor.