What allowed warships to grow longer?

What innovation allowed warships to become so much longer?

Improved metallurgy and progressively stronger, more effective steel enabled longer warship hulls.

Improved metallurgy allowed warships to grow longer. Stronger and more effective steel let naval architects build longer hulls without unacceptable structural weakness. Material science therefore set an important limit on ship scale. Structural possibility and safe operating practice do not always advance at the same rate.