Why horsepower alone did not make aircraft faster

The discussion contrasts the Napier Lion and other contemporary engines with later powerplants to show why raw horsepower is only part of the design problem. A very heavy engine could consume too much of an aircraft's weight allowance even if it delivered impressive power. The thousand-horsepower Napier Cub weighed nearly 2,500 pounds dry, while a later Merlin could produce comparable power at roughly half that weight. The huge Blackburn Cubaroo demonstrates how an engine's mass and cost could drive an entire airframe rather than simply improve an existing design. This power-to-weight constraint shaped the pace at which torpedo aircraft could gain speed, range, and payload.