Navigation and interception problems for a nuclear torpedo

A very long-range nuclear torpedo is frightening if it works, but seabed collision, uncertain navigation, and the difficulty of arranging an anti-torpedo intercept complicate both attack and defense.

Question

How credible is a nuclear-powered, nuclear-armed torpedo as a weapon, and how could it be stopped?

Short answer

It is dangerous if it reaches the target, but long underwater navigation and seabed hazards threaten it, while interception requires rare anti-torpedo weapons and favorable geometry.

Notes

The weapon's destructive payload is only one part of the problem; it must also complete a long underwater journey. Conventional countermeasures may have little effect on a torpedo that ignores distractions and continues toward a geographic target. An anti-torpedo torpedo offers a possible defense, but the intercept geometry is tight and few suitable systems can be deployed quickly from aircraft or helicopters. Collision with the seabed or continental slope is a major practical threat to the attacking weapon itself. A fast Spearfish-class torpedo might offer a better intercept chance than slower alternatives, yet success still depends on having a platform in the right place.