(a) In time of war or when war is imminent, the Secretary of the Army may acquire by lease any building, or part of a building, in the District of Columbia that may be needed for military purposes.

(b) At any time, the Secretary may, for the purposes of the Department of the Army, requisition the use and take possession of any building or space in any building, and its appurtenances, in the District of Columbia, other than

The Secretary shall determine, and pay out of funds appropriated for the payment of rent by the Department of the Army, just compensation for that use. If the amount of the compensation is not satisfactory to the person entitled to it, the Secretary shall pay 75 percent of it to that person, and the claimant is entitled to recover by action against the United States an additional amount that, when added to the amount paid by the Secretary, is determined by the court to be just compensation for that use.