Compound engines, triple expansion, and coal endurance

Victoria's machinery illustrates the change from compound to triple-expansion steam engines. A compound engine expanded steam through high- and low-pressure cylinders. Stronger steel boilers allowed higher steam pressures, making an intermediate-pressure stage practical. The extra expansion extracted more energy from the same coal and gave Victoria considerably more power than Camperdown. That efficiency could provide longer range for the same bunker load or free weight for armor. Propulsion efficiency therefore affected naval logistics as directly as ship performance.