How the Invincibles reached 25 knots

The Invincibles displaced about 17,500 tons normally and nearly 21,000 tons at deep load, figures not far removed from Dreadnought. Their machinery plant expanded to thirty-one water-tube boilers driving four shafts with about 41,000 shaft horsepower. That power pushed the somewhat lighter ships to 25 knots, roughly four knots faster than Dreadnought. Invincible, Indomitable, Inflexible, Indefatigable, New Zealand, and Australia are presented as stages in a developing British battlecruiser lineage. This combination of heavy guns and speed created a wider strategic shock than Dreadnought alone.