River-class frigates bring sloop capability to more shipyards

Black Swan-class sloops supplied strong anti-submarine capability, but fewer yards could build them than could produce Flower-class corvettes. The River design sought more range and operational flexibility without losing access to that wider industrial base. Reciprocating expansion engines avoided dependence on turbine manufacture. Naval architect William Reed adapted the escort requirement to a design suited to merchant-building methods. Its success came from matching the desired fighting capability to machinery and shipyards that could deliver ships in quantity.