River-class OPVs continue the historical sloop role

What historical warship type was closest in capability to a modern River-class OPV?

The sloop, especially types such as the Black Swan class, because it combined economical patrol and presence work with adaptable escort duties.

The sloop is offered as the closest historical equivalent to a River-class offshore patrol vessel, with the Black Swan class suggested as an example. The comparison concerns the general role rather than identical weapons or crew size. Older sloops tended to carry more equipment and more flexible armament, supported by somewhat larger crews. A modern OPV could also receive additional weapons, so its present fit need not define every possible use of the hull.