The practical minimum for an air-defence corvette

Could a cheap air-defence missile boat protect a harbor, and what would its minimum characteristics be?

A capable radar and missile battery would probably require roughly 2,500 to 3,000 tons, frigate-grade sensors, CAMM or a comparable missile, and perhaps two 76 mm guns.

An effective air-defence radar is expensive and needs substantial electrical power. Those requirements push the proposed harbour-defence boat toward roughly 2,500 to 3,000 tons with a radar normally found on a frigate. The suggested armament includes CAMM or a comparable missile and perhaps two 76 mm guns. Land-based air defence is offered as an alternative. At a sufficiently large port, a floating battery could carry its equipment together and reposition on the seaward side.