(b)
Whenever a statute of the United States provides for a maritime action in rem or a proceeding analogous thereto.
Except as otherwise provided by law a party who may proceed in rem may also, or in the alternative, proceed in personam against any person who may be liable.
Statutory provisions exempting vessels or other property owned or possessed by or operated by or for the United States from arrest or seizure are not affected by this rule. When a statute so provides, an action against the United States or an instrumentality thereof may proceed on in rem principles.