Cruisers were large enough to yield useful machinery and structural lessons, yet numerous enough that one disappointing ship would not imperil the battle fleet. Before the treaty era they also carried less national prestige than capital ships. The Calliope-class studies compared mixed and homogeneous batteries and installed Parsons geared turbines in Calliope and Champion. Champion's two-shaft machinery produced about 41,000 shaft horsepower and 29.5 knots, showing that a cruiser programme could test machinery before wider adoption.
Chapter · 30:40-34:20
Light cruisers as experimental engineering platforms
Cruiser programmes gave d'Eyncourt room to test armament layouts, protection, and geared turbines at lower strategic risk than a battleship experiment.