Antiaircraft gun carriage. Assembling the traversing gear and bearing on a thirty-seven millimeter antiaircraft gun carriage. These precision-built ball bearing installations are vitally important, for on their unfailing smooth operation depends the gunners' ability to follow his swiftly moving target. War program production scene in one of Pennsylvania's heavy industry plants now converted to the production of vitally needed military equipment. AETNA. Ellwood City, Pennsylvania