The projected class included ships such as Battleaxe, Broadsword, Crossbow and Scorpion, and was much larger than the group that eventually entered service. It was designed with operations around Japan in mind and needed to keep more ships working through damage. Dividing the boiler and turbine rooms into units made it harder for a single hit in the machinery spaces to disable the whole plant. That emphasis on survivability was a second reason for the design alongside the wish to use available yard capacity.
Notable Point · 1:29:30-1:30:27
Why the Weapon class separated its machinery into units
The Weapon class arranged boiler and turbine spaces in separate units to limit the effects of a hit.