The attack on Pearl Harbor was a surprise military strike by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, in the United States Territory of Hawaii, on the morning of December 7, 1941.The attack led to the United States' entry into World War II.reliminary planning for an attack on Pearl Harbor to protect the move into the Southern Resource Area (the Japanese term for the Dutch East Indies and Southeast Asia generally) had begun very early in 1941 under the auspices of Admiral Isoroku Yamamoto, then commanding Japan's Combined Fleet.