Pearl Harbor Naval Station (PHNS) is on the island of Oahu, Hawaii. It spans over 13,107 acres and is currently the headquarters of the U.S. Pacific Fleet. It was built in 1911 and steadily expanded throughout 1919. By 1933, the U.S. began growing concerned about Japan’s intentions as the Japanese military was at war with China. As a defensive exercise, The U.S. Navy staged a mock attack on the naval station to test preparedness. The attack succeeded and the defense was deemed “a failure”. It is now called Joint Base Pearl Harbor-Hickam because in years following WWII, Pearl Harbor merged with Hickam Air Force Base. It is still an active base today. The Japanese attack on Pearl Harbor on December 7, 1941 was the trigger that made the United States enter into WWII.