Pearl Harbor, or Puuloa, is a lagoon harbor on the island of Ookinaahu (Oahu), Hawaiokinai (Hawaii), west of Honolulu (Honolulu, Hawaii). Much of the harbor and surrounding lands is a United States Navy deep-water naval base. It is also the headquarters of the U.S. Pacific Fleet (United States Pacific Fleet). The attack on Pearl Harbor by the Empire of Japan on December 7, 1941, brought the United States into World War II.