Its modern incarnation dates from the splitting of the United States Fleet up into the Atlantic, Pacific and Asiatic fleets prior to World War II. Until May of 1940, this unit was stationed on the west coast of the United States, at which point it transferred to Pearl Harbor, Hawaii. At the outbreak of the war, the commander of this fleet was Admiral Husband E. Kimmel.
At this time, the fleet consisted of 9 battleships, 3 aircraft carriers, 12 heavy cruisers, 8 light cruisers, 50 destroyers, 33 submarines, and 100 patrol bombers. This was approximately the unit's strength at the time of the Japanese attack on Pearl Harbor.
See also:
Composition of the Pacific Fleet -- May 1941