Coastal defence ships as armor-firepower deterrents

This section sets up coastal defence ships as vessels built around the armor-and-firepower side of the classic warship design triangle. The key point is economic and operational: a navy defending ports or nearby waters can worry cruisers, and sometimes battleships, without buying the expensive machinery needed for high speed. Propulsion plants, gearing, and turbines impose costs that are less visible than guns or armor. A simpler, lower-powered engine is also easier and cheaper to maintain than machinery designed for sustained high speed. That makes the type a local deterrent rather than a fleet unit intended to chase enemies across oceans.