Shipping on United States Vessels.—

Sec. 509. Shipping on United States Vessels.— Such steps as may be necessary shall be taken to assure, as far as practicable, that at least 50 per centum of the gross tonnage of commodities, materials and equipment procured out of funds made available under sections 103, 123, 131, 132 (a), 201, 304, and 403 of this Act and transported to or from the United States on ocean vessels, computed separately for dry bulk carriers, dry cargo liner and tanker services and computed separately for section 103, and for sections 123, 131, 132 (a), 201, 304, and 403 (taken together) is so transported on United States flag commercial vessels to the extent such vessels are available at market rates for United States flag commercial vessels provided such rates are fair and reasonable; and, in the administration of this provision, steps shall be taken, insofar as practicable and consistent with the purposes of this Act, to secure a fair and reasonable participation by United States flag commercial vessels in cargoes by geographic area.