Golden Gate National Recreational Area - An Integrated System of Guns (U.S. National Park Service)

San Francisco's harbor defenses relied on a complex system of guns, underwater mines, and antisubmarine nets. Central to the system were guns of many sizes, each with its own purpose. These guns were classified by the diameter of the projectiles they fired.

San Francisco History Center, San Francisco Public Library

Rapid-fire three-inch (above) and 90 mm guns targeted aircraft and motor torpedo boats. Smaller 40 mm and various caliber machine guns were used as antiaircraft (AA) weapons.

PARC, Golden Gate National Recreation Area

Mortars could fire 12-inch shells on a high arcing trajectory, thereby penetrating the lightly armored decks of ships. Mortars also could fire in all directions, making them useful during a ground invasion.

San Francisco History Center, San Francisco Public Library

Six-inch guns, like this one at Battery Chamberlin, protected the offshore minefields. Mounted and mobile 155 mm guns also guarded the minefields and protected the beaches from landing craft.

PARC, Golden Gate National Recreation Area

Massive 16-inch guns at Battery Townsley (as seen above) and Davis defended against batteships that also had guns capable of firing shees up to 25 miles.

San Francisco History Center, San Francisco Public Library

Turn-of-the-century 10- and 12-inch guns and newer, high-powered 12-inch guns at Battery Wallace fended off armored warships in the 10 to 15 mile range.