Why subdivision matters to battlecruiser survival

Early lightly protected armored cruisers, later battlecruisers, fast battleships, and full battleships form a spectrum of increasing structural density. More subdivision creates a honeycomb of compartments, improves damage tolerance, and provides more structure from which armor can be supported over a wider area. Two ships may quote the same maximum belt thickness while protecting very different portions of the hull. That is why the rebuilt Kongo-class ships can prompt a classification debate, while the Scharnhorst class remains a fast-battleship design despite its 11-inch guns: the armament reflected German industrial timing and a planned later upgrade rather than a lightly built hull. The Scharnhorsts fit with the Dunkerque class, while Germany's First World War battlecruisers remain battlecruisers because their subdivision and armor coverage did not reach fast-battleship standards. The same principle explains why larger modern hulls can sometimes carry more redundancy and survivability than a distributed collection of small specialized vessels.