The class's 25-knot maximum suited the pre-dreadnought fleet, where 18-knot battleships and similarly fast destroyer flotillas left a scout room to manoeuvre. It became restrictive once dreadnoughts made 21 knots and battlecruisers aimed for 28. A cruiser leading destroyers or accompanying the battle fleet needed a margin of speed so that it would not restrain the force. The four funnels reflect the airflow and exhaust demands of machinery that designers were still learning to manage, while small-tube boilers had yet to enter Royal Navy service. More speed might have forced a larger hull and greater technical risk, so 25 knots was a defensible short-term choice. The pace of change from 1905 to 1914 made that caution costly, and the entire scout-cruiser type was soon overtaken.
Chapter · 7:25-12:05
Why 25-knot scout cruisers fell behind the battle fleet
A 25-knot scout cruiser could lead destroyers in the pre-dreadnought era, but could not comfortably keep pace once fast battleships and battlecruisers transformed fleet speed.