Watching the North Pacific: British and Commonwealth intelligence before Pearl Harbor

Abstract

Historians have long questioned the extent to which British Intelligence knew about Japan's impending operations on the eve of the Pacific War. An examination of archival sources from Britain, Canada and the United States, as well as credible post-war testimony from former participants in Second World War intelligence operations, produces several conclusions. Throughout 1941, British Intelligence pointed to a war with Japan in South-East Asia. On the eve of the Pacific War, intelligence staff of the British Commonwealth monitored the vast expanses of the North Pacific. Apart from anticipating conflict in South-East Asia, British Intelligence, according to some sources, also suspected that a Japanese attack on Pearl Harbor was imminent, an assessment shared with the United States.