On back: "SAN FRANCISCO-OAKLAND BAY BRIDGE; Walter G. Swanson; 500 Sansome St. - GA rfield 1415. File 900.11 B-12/BD. View showing Caisson W-4 (right of photo) at Moore Dry Docks, Oakland, ready for towing to pier site. Caisson W-4, the World's Largest Caisson, having 55 fifteen foot diameter dredging well cylinders, is shown with steel domes in place for air flotation control. This Caisson now forms the base of Pier W-4, the Concrete Center Anchorage. Caisson W-3 (left of photo) is shown with the cutting edge section and also the cylinder adaptor sections in place. Caisson W-3 contains 28 fifteen foot cylinders. It now forms the base of Pier W-3."
