The Russian government has recently created a fleet of underwater, automated torpedoes. They have a 200 Megaton nuclear payload each, with highly radioactive cobalt included in the warhead. They are deployed along the seabed, waiting for an activation signal. When detonated, they trigger a 500m high tsunami that could push dozens of miles inland, irradiating everything it its path.

They are designed so that after slowly approaching the target. they suddenly move at over 100 mph using supercavitation. This makes it very difficult to detect or intercept them.

What possible countermeasure could you develop to either mitigate the destruction or neutralize the torpedo before it reaches its target?