46 U.S.C. § 31102: Waiver of immunity

(a) In General.—A civil action in personam in admiralty may be brought, or an impleader filed, against the United States for—(1) damages caused by a public vessel of the United States; or (2) compensation for towage and salvage services, including contract salvage, rendered to a public vessel of the United States. (b) Counterclaim or Setoff.—If the United States brings a civil action in admiralty for damages caused by a privately owned vessel, the owner of the vessel, or the successor in interest, may file a counterclaim in personam, or claim a setoff, against the United States for damages arising out of the same subject matter.