46 U.S.C. § 30911

(a) In General .— A judgment against the United States or a federally-owned corporation under this chapter may include costs and interest at the rate of 4 percent per year until satisfied. Interest shall run as ordered by the court, except that interest is not allowable for the period before the action is filed. (b) Contract Providing for Interest .— Notwithstanding subsection (a), if the claim is based on a contract providing for interest, interest may be awarded at the rate and for the period provided in the contract.