Oil-fuelled hull efficiency and space for later upgrades

Why did the Revenge class use about 3,000 tons less steel than the Queen Elizabeth class?

The oil-first Revenge design used its hull more efficiently, while the Queen Elizabeths' coal-derived layout left extra space that later helped their upgrades.

The Revenge class is described as a more efficient design because its hull was arranged around oil firing. The Queen Elizabeths had been conceived for coal before the change to oil, leaving inefficiencies in their structure. That extra space also had an advantage: it made the Queen Elizabeths easier to upgrade than the Rs. A layout that saved material initially could offer less room for later alterations.