Torpedo defense

Torpedo defense concerns the entire field of strategies, tactics, and practices which are intended to thwart the combat effectiveness of torpedoes. Torpedoes are subsurface naval weapons whose movement is limited to the underwater environment. As such, torpedoes are generally intended for attacking naval assets - broadly separated into surface ships, submarines, and potentially other waterborne assets (coastal installations such as floating docks, floating oil platforms, bridge foundations). The strategies for torpedo defense can dramatically differ for these categories, and the specific constituents thereof.

Such strategies include stealth, evasive maneuvers, passive defense like torpedo belts, torpedo nets, torpedo bulges, and sonar torpedo sensors, "soft-kill" active countermeasures like sonar decoys and sonar jammers, and "hard-kill" active defenses, like anti-torpedo torpedoes similar in idea to missile defense systems. Surface Ship Torpedo Defense and Countermeasure Anti-Torpedo systems are highly experimental and the US Navy ended trials on them in 2018.

As stated, defenses can be broadly classed as passive, active, and stealth-based. Strategies can be classed as reactive (undertaken after an enemy torpedo launch) and proactive (also known as nonreactive, undertaken before an enemy torpedo launch). Further, the interdiction of a torpedo can be either classed as a soft kill or a hard kill. Soft kill refers to a partial or total reduction of the weapon's combat effectiveness, such as by distracting it with countermeasures or causing it to waste time until its propulsion system runs out of mobile endurance. Hard kill refers to a physical incapacitation of the weapon with damage.

As with all other defensive measures, torpedo defense falls under the categorization of the "survivability onion". The first lines of defense are always stealth and distance, ideally beyond any hope of engagement by the enemy. Secondary to these are speed and agility, the capacity to evade. These also include the emerging field of hard-kill countermeasures, which are kinetic interceptors designed to destroy or incapacitate the incoming torpedoes. The final lines of defense are various designs of armor, sheer size and bulk which can shrug off localized damage, and resiliency modifications such as distributed flotation compartments.