Choosing ship size for a diplomatic mission

How small can a warship be and still serve as a useful diplomatic tool?

It depends on the mission: an OPV can be useful in lower-risk presence work, but a contested sea may require a bigger and better-armed ship.

A River-class offshore patrol vessel can handle fisheries protection, Gibraltar, the Falklands, and other lower-risk presence missions. Its modest size does not prevent it from showing a flag, enforcing routine rules, or sustaining a visible national commitment. A South China Sea deployment demands a larger and better-armed ship because the diplomatic signal and operational danger are different. The mission, opponent, and acceptable risk determine the useful ship size for naval diplomacy.