What offshore patrol vessels do in a major war

What roles would offshore patrol vessels perform during a major war?

They would cover secondary theaters, presence, disaster relief, and continuing maritime-security duties, with some hulls adaptable for convoy escort or mine warfare.

A major war leaves secondary theatres, disaster relief, and routine maritime-security work to be covered while larger combatants concentrate elsewhere. Piracy and attacks on shipping do not disappear, and an opponent could support disruptive groups to keep those demands high. Some OPVs could take on convoy escort or mine-warfare work if the necessary equipment were available. The historical comparison is with older pre-dreadnoughts sent to the Persian Gulf and Red Sea, where their remaining combat power could still exceed the local threat. Adequate ships in those roles released newer units for other duties.