The attack on Pearl Harbor was an unannounced military strike conducted by the Japanese navy against the United States naval base at Pearl Harbor, Hawaii on the morning of December 7, 1941. It resulted in the United States' entry into World War II. The attack was intended as a preventive action in order to keep the U.S. Pacific Fleet from influencing the war that the Empire of Japan was planning in Southeast Asia, against Britain and the Netherlands, as well as the U.S. in the Philippines. The attack consisted of two aerial attack waves totaling 353 aircraft, launched from six Japanese aircraft carriers.