A 28-knot ship facing a 21-knot battleship could choose the range of an engagement and threaten attacks from different directions. Combining that speed with battleship armour and heavy guns required machinery with a better power-to-weight ratio than contemporary plants reliably offered. High-pressure steam plants of the late 1930s and early 1940s would make that combination easier. A hypothetical Queen Elizabeth with enough oil-fired, small-tube boilers suggests an earlier route to 28 knots, but the necessary improvements still lay ahead. Designers could not know when those improvements would arrive, so navies had to order ships using the technology available.
Notable Point · 46:56-50:53
Why the fast battleship was still a technological gamble
A true fast battleship was already desirable, but machinery weight and uncertainty about the next propulsion breakthrough kept it just beyond reliable pre-war design practice.