Amends the Merchant Marine Act, 1936 to provide that when the 20 year period during which vessels operating exclusively in specified foreign trade and for which a construction-differential subsidy was received for restricting voyages exclusively to such trade ends, the requirements and restrictions for receipt of such subsidy, including making payments for violating the restriction on engaging in domestic trade also ends. (Currently, termination of such period does not affect the requirement to make such payments.)