((a)) ** .—** 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)) ** .—** 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.