Nation: Deep Hunting

It was enough to give a submarine skipper the shakes: the U.S. Navy announced that it is adding to its arsenal the Mark-46 torpedo, a solid-fuel missile with an underwater speed faster than the newest nuclear subs. Thanks to the wonders of computerdom, the Mark-46 also has a built-in, all-but-infallible killer’s instinct.

The torpedo can be launched either from aircraft or surface ships. It dives to a preset depth, speeds around in large circles, using secret, supersophisticated devices to seek out an enemy sub. If it finds nothing, the Mark-46 switches to “active echo ranging,” breaks its circular pattern and snakes zigzag through the water like a hunter stalking a deer. Once the enemy is located, the torpedo homes in with its sonar.

In tests off San Diego, the Mark-46, equipped with dummy instead of high-explosive warheads, sought out and struck highly maneuverable nuclear submarines with unerring accuracy. One especially determined Mark-46 survived its initial collision and proceeded to slam again and again into the target sub. To escape damage to his boat, the skipper swiftly surfaced; the Mark-46 is prevented by its programming from returning to shallow depths, where it might turn upon and destroy the ship that fired it.

According to Navymen, there is only one thing that the Mark-46, which will be delivered to U.S. antisubmarine groups by summer, cannot do. That is to tell the difference between friendly and hostile submarines. So the Navy will use the weapon only in waters where none of its own submarines are operating.