The Secretary of Transportation is authorized to have constructed in shipyards in the continental United States such new vessels as he shall determine may be required to carry out the objects of this chapter, and to have old vessels reconditioned or remodeled in such yards: Provided, That if satisfactory contracts for such new construction or reconstruction, in accordance with the provisions of this chapter, cannot be obtained from private shipbuilders, the Secretary of Transportation is authorized to have such vessels constructed, reconditioned, or remodeled in United States navy yards. For the purposes of this section, the term “continental United States” includes the States of Alaska and Hawaii.