Why a new scout role kept old engines

The class retained triple-expansion engines despite the public demonstration of Turbinia at the 1897 Spithead Review and the arrival of the turbine-powered destroyers HMS Cobra and HMS Viper. Both destroyers suffered accidents, but their turbines were not treated as the cause. This was radical conservatism: the Royal Navy tested a new mission with familiar weapons and engines to reduce technical risk. That caution undermined the concept because a scout and destroyer-support ship needed enough speed to range ahead and keep pace with faster flotillas. HMS Dreadnought raised battle-fleet speed to about 21 knots while destroyers approached 30. The Sentinel class's useful speed margin was disappearing. The later 1910 Town-class light cruisers adopted turbines, but the Royal Navy and taxpayers first paid for a generation that became operationally dated very quickly.