As a condition of designating a vessel as an American Great Lakes vessel under this section, the Secretary shall require the person who will be the owner of the vessel at the time of that designation to enter into an agreement with the Secretary which provides that if the Secretary determines that the vessel is necessary to the defense of the United States, the United States Government shall have, during the 120-day period following the date of any revocation of such designation under section
1241t of this Appendix, an exclusive right to purchase the vessel for a price equal to—
whichever is greater.