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One of the major needs in modern multi-threat naval warfare are more robust torpedo defence systems. Several nations are currently pursuing both national programmes and joint programmes to improve ship survivability against an attack from a heavy weight torpedo (HWT).
Most major offensive weapon systems have a countermeasure (CM) or counter weapon which can defeat an attack against a surface combatant, amphibious ship, or aircraft carrier. Antiair warfare (AAW) systems such as AEGIS defend against anti-ship missiles (ASM) by using decoys, electronic support measures (ESM), electronic countermeasures (ECM), surface-to-air missiles (SAM), other aircraft and guns. In the anti-surface role the gun is typically out ranged by the far more lethal surface-tosurface missile (SSM). The HWT is one weapon where the offensive capability to destroy a target exceeds the current defensive systems ability to defeat an attack. Robust defensive capability, for surface ships, includes the continued application of the defence-in-depth concept. This concept utilizes many elements to provide effective defence ranging from anti-submarine warfare (ASW), stealth (signature control ranging from acoustics, to IR to RF emission control), manoeuvre, decoys, countermeasures and finally if all else fails, hardkill weapons. The types of hardkill weapons available may include depth bombs delivered by rocket or mortar to anti-torpedo torpedo (ATT).
THE THREAT
The urgency of need for a robust system is illustrated in properties of the sea and the extreme difficulty of detecting a submerged vessel or weapon in the ocean or littoral seas. Additionally, the HWT is a true sinking weapon. It maximizes the use of physics (very large warhead and incompressible water) to break the keel, destroy buoyancy, kill a large portion of the crew, and quickly sink the ship. As a comparison, mines and cruise missiles produce relatively fewer casualties than torpedoes do. For example, the USS Stark (FFG-31 ) was struck by two Exocet air launched cruise missiles, resulting in 37 dead and the USS Samuel B. Roberts (FFG-58) struck one contact mine resulting in no deaths. Both vessels returned to service. A HWT will sink a frigate or destroyer-sized vessel in only a few minutes. A larger vessel will take just a little longer to sink. Both will result in severely high casualty rates. In 1971 a Pakistani submarine attacked the INS Khukri...