The labels describe operational relationships rather than a universal speed threshold. A fast battleship must keep contact with the fleet's cruiser screen so it can support the scouting line in action. A battlecruiser needs enough extra speed to move beyond that screen and conduct independent reconnaissance or interception. British practice used a cruiser-line benchmark near 28 knots, and other navies commonly measured their ships against Royal Navy equivalents. A 24-knot battle line in this scenario could push the cruiser standard towards 30 knots. Queen Elizabeth-class ships might then reach 28 knots if they fell short of that target, or 30 knots if sustained small-tube-boiler work succeeded.
Notable Point · 2:57:12-2:59:19
Fast battleships and battlecruisers have different speed jobs
A fast battleship must maintain contact with the cruiser line, while a battlecruiser must outrun that line for independent reconnaissance.