The first forms of anti-torpedo protection

What was the first anti-torpedo device used to protect ships?

Double bottoms were an early response to underwater mines; against self-propelled torpedoes, nets were the first direct protective device.

The earliest protection depends on whether 'torpedo' means a mine or a self-propelled weapon. Double and triple bottoms are proposed as an early response to underwater mine explosions, although their structural advantages complicate assigning a single reason for their adoption. Protection against mines helped justify the additional cost. Against self-propelled Whitehead torpedoes, nets were the first direct protective device identified. Later degaussing cables reduced the magnetic signature that could trigger influence weapons.