A battleship emphasizes armour and heavy firepower, while a battlecruiser trades some protection for the speed needed to choose or avoid engagements. In this period, roughly 28 knots marks a useful threshold for a fast battleship, though it is not a universal rule. First World War fleets could sustain separate types for distinct jobs, but treaty limits made every capital-ship slot scarce. Combining roles offered greater versatility when a navy could no longer build as many specialist ships as it wanted.
Notable Point · 39:33-41:05
How treaty limits encouraged the fast-battleship compromise
A fast battleship blends battleship protection with battlecruiser speed, a compromise that grew more attractive once treaties limited separate specialist types.