Well before the attack on Pearl Harbor, California was mobilizing for war. The Army began to acquire land to expand existing installations and build new posts, training areas, and airfields. The Pacific Fleet was deployed to Pearl Harbor in order to better counter the Japanese threat. Soon the sight of antiaircraft and coastal defenses, long convoys on the roads, and thousands of service members became common throughout most of the state.
The California National Guard was ordered to a year of active duty in the spring of 1941. The state government soon organized its own armed forces under the State Guard Act of 1940.
Over 75,000 Californians served in the State Guard while thousands more served in over 300, local licensed militia companies of the State Militia. Local governments also formed defense councils to coordinate their actions.
Thousands also served in the Civil Defense, Aircraft Warning Service, and other volunteer auxiliaries.