The attack on Pearl Harbor was a surprise military strike by the Imperial Japanese Navy Air Service upon the United States (a neutral country at the time) against the naval base at Pearl Harbor in Honolulu, Territory of Hawaii, just before 08:00, on Sunday morning, December 7, 1941. The attack led to the United States' formal entry into World War II the next day. The Japanese military leadership referred to the attack as the Hawaii Operation and Operation AI, and as Operation Z during its planning. Japan intended the attack as a preventive action to prevent the United States Pacific Fleet from interfering with its planned military actions in Southeast Asia against overseas territories of the United Kingdom, the Netherlands, and those of the United States. Over the course of seven hours there were coordinated Japanese attacks on the U.S.-held Philippines, Guam, and Wake Island and on the British Empire in Malaya, Singapore, and Hong Kong.