The defense of San Francisco Bay was of paramount importance during World War II. Not only was there a large civilian population and interior agricultural industry to be protected, but there were major military and industrial complexes in the Bay Area that were prime targets for Japanese attack.
Many of the troops and supplies for the Pacific theater passed through the bay and the Golden Gate on their way to the Pacific Theater. Military infrastructure in the area included Fort Mason, which was the port of embarkation for over a million soldiers during the war, and the Presidio, from which the defense of the Pacific Coast was run. Treasure Island and Alameda Naval Air Station were important naval bases. Liberty ships built by the hundreds at the Kaiser Shipyards in Richmond, California, were loaded with cargo, food, medical supplies, tanks, guns, and construction equipment at the ports of San Francisco and Oakland. Hunter's Point and Mare Island Navy shipyards made ships and landing craft used on the many amphibious landings during the war. The local shipyards also repaired and serviced many of the ships and submarines from the Pacific Theater. Port Chicago was a critical ammunition supply depot. All these vessels had to pass through the narrow Golden Gate Straits.
To protect the crucial Golden Gate and Bay Area harbors, an integrated coastal defense system was constructed. This system of weapons, fire control, mines, nets, and men were all that kept the vital life line from San Francisco bay open to supply the men and women of the Pacific Theater.