A naval vessel that is in excess of 3,000 tons or that is less than 20 years of age may not be disposed of to another nation (whether by sale, lease, grant, loan, barter, transfer, or otherwise) unless the disposal of that vessel, or of a vessel of the class of that vessel, is authorized by law enacted after August 5, 1974. A lease or loan of such a vessel under such a law may be made only in accordance with the provisions of chapter 6 of the Arms Export Control Act (22 U.S.C. 2796 et seq.) or chapter 2 of part II of the Foreign Assistance Act of 1961 (22 U.S.C. 2311 et seq.). In the case of an authorization by law for the disposal of such a vessel that names a specific vessel as being authorized for such disposal, the Secretary of Defense may substitute another vessel of the same class, if the vessel substituted has virtually identical capabilities as the named vessel. In the case of an authorization by law for the disposal of vessels of a specified class, the Secretary may dispose of vessels of that class pursuant to that authorization only in the number of such vessels specified in that law as being authorized for disposal.