At the bottom of the Thames River last week, Navy divers dug up
the sensors and cables that measure magnetic signatures of
military ships and submarines. Even though the Navy is replacing
the 20-year-old underwater range with a new one, most people
don't know the range exists. And even those who have heard about
it sometimes don't understand what it really does. A steel-
hulled ship is surrounded by a magnetic field. As the ship moves
through the water and traverses the Earth's natural magnetic
fields between the North and South poles, the ship's magnetic
field changes. The Navy checks its vessels to make sure the
magnetism present in the hulls will not trigger magnetic mines
or make the ships easier to detect. The only Magnetic Silencing
Facility in the Northeast is operated by the Naval Submarine
Base in Groton. When military ships pass over the sensors and
cables at the center of the channel, the information is
converted into a computer file and Preston E. Tone-Pah-Hote Jr.,
who oversees the range operation