Review: Pearl Harbor is a simple harbor on the island of Oʻahu, Hawaii, west of Honolulu. Much of the harbor and surrounding lands is a United States Navy deep water naval base: headquarters of the U.S. Pacific Fleet. Pearl Harbor was originally an extensive, shallow embayment called Wai Momi (meaning "water of pearl"). The attack on Pearl Harbor was a surprise attack. On the morning of December 7, 1941, planes and midget submarines of the Imperial Japanese Navy began a surprise attack on the U.S.