((a)) ** .—** It is necessary for the national defense and the development of the domestic and foreign commerce of the United States that the United States have a merchant marine—

((1)) sufficient to carry the waterborne domestic commerce and a substantial part of the waterborne export and import foreign commerce of the United States and to provide shipping service essential for maintaining the flow of the waterborne domestic and foreign commerce at all times;

((2)) capable of serving as a naval and military auxiliary in time of war or national emergency;

((3)) owned and operated as vessels of the United States by citizens of the United States;

((4)) composed of the best-equipped, safest, and most suitable types of vessels constructed in the United States and manned with a trained and efficient citizen personnel; and

((5)) supplemented by efficient facilities for building and repairing vessels.

((b)) ** .—** It is the policy of the United States to encourage and aid the development and maintenance of a merchant marine satisfying the objectives described in subsection (a).