Power density, armor coverage, and subdivision

The progression from Invincible through Lion, Queen Mary, and Tiger reflects increasing machinery power density. Designers could spend that improvement on still more speed or use hull volume and weight for armor coverage and subdivision. Internal bulkheads could keep blast, flooding, and equipment damage on one side of a compartment boundary, sometimes turning catastrophic damage into shock that a crew could work through. Survivability therefore depended on protected volume and compartmentation as well as nominal armor thickness. Added subdivision, however, could complicate efficient machinery layouts and long-range cruising.