How did the Whitehead torpedo threaten armoured warships?

The Whitehead torpedo posed a significant threat to armoured warships by targeting their vulnerable underwater hulls, effectively bypassing the heavy belt armour designed to protect against surface-level shell fire.12

Developed by Robert Whitehead, this self-propelled weapon carried an explosive charge directly to an enemy vessel. Because traditional armour was primarily concentrated on a ship's sides and superstructure to deflect big-gun projectiles, the underwater impact of a torpedo created a critical vulnerability. The threat was so severe that it forced naval architects to fundamentally alter warship design, leading to the implementation of internal compartmentalization and external "blisters" or bulges intended to absorb the shock of underwater explosions and keep them at a distance from the ship's interior.3142

This rivalry between the big gun and the torpedo became a primary driver of naval development from the late 19th century through World War I, compelling designers to balance offensive firepower with increasingly complex underwater protection systems.5