The class was not mechanically uniform: Babcock & Wilcox and Foster Wheeler supplied different boiler arrangements. Four ships used the period's conventional 220-volt direct-current system, while four received 440-volt three-phase alternating current. Those choices combined into four machinery-and-electrical variants across only eight ships. The programme had that unusual freedom because destroyers attracted less political scrutiny than cruisers, carriers, and major conversion projects.
Notable Point · 6:20-9:07
Why eight Darings contained four machinery combinations
Different boiler makers and 220-volt DC or 440-volt AC systems left the eight-ship class with four overlapping machinery and electrical arrangements.