The Contractor shall make for the Government the following articles hereinafter called "the articles," namely: Five hundred (500) U. S. A. standardized 12-cylinder aircraft engines, in accordance with the drawings and specifications attached hereto, and further identified in the order hereto attached, including all authorized changes thereof, and to deliver the same f. o. b. the Contractor's works, packed for shipment in the manner covered by the specifications, and, as nearly as possible under existing circumstances, at the times and in the quantities hereinafter set forth or as set forth in the order hereto attached, and the Government shall accept the articles and pay therefor, all upon the terms and conditions in this contract set forth.