The wartime requirement was for more capability than a corvette without making every escort a fully naval-built sloop. A mixture of civilian and naval construction practices widened the available shipbuilding base. Twin screws and shafts improved on the predominantly single-shaft corvettes. The resulting ships gained a lasting reputation as cheaper, less demanding alternatives to destroyers. That reputation arose from specific industrial choices, so it cannot establish the cost or survivability of a modern frigate by itself.
Notable Point · 3:47-5:07
How wartime construction made frigates the cheaper option
The modern frigate's economical reputation began with a construction compromise that let more civilian yards build capable convoy escorts.