The later D-class grouping contained nine surviving two-funnel Thornycroft destroyers built around a 30-knot requirement. A tenth ship had been lost before the grouping formed, so the administrative count differed from the number built. Thornycroft treated the specified speed as a floor and refined the bow and underwater form to reduce resistance. Extra speed could emerge within safe machinery limits, sometimes even within the specified operating margins and steam pressure. At high power, its destroyers could rise slightly in the water and outperform ships with similar machinery. This work helped show how hull shaping could improve speed alongside machinery development.
Notable Point · 29:36-32:21
D-class hull shaping and real speed
Thornycroft's two-funnel D-class destroyers showed how careful hull shaping could turn a nominal speed requirement into better real performance.