Turreted cruisers require metallurgy and horsepower

Turret concepts existed before the American Civil War, with drawings reaching back to the later Napoleonic Wars. The idea alone could not make a practical seagoing warship. Metallurgy had to support the structure and weapons, while steam machinery had to deliver enough power to move their weight. These developments allowed monitor turrets to be combined with broadside arrangements. They also opened the path toward warships armed entirely in turrets.