Armor-grade steel constrained early dreadnought construction

What was one of the major industrial hurdles in building the early dreadnoughts?

Producing and rolling the enormous quantity of steel and armor plate the ships required.

Steel production, rather than a novel weapon or layout, was a major industrial bottleneck. Dreadnought programs required shipyards and suppliers to roll very large quantities of steel, including armor plate, making heavy industrial capacity part of the naval arms race.