The sonar equipment showed what kind of rock it was—iron and basalt.
But what good would it do anyone to stick a sonar device on an island like this?
For instance, there must have been a sonar unit near where we swam at St. Thomas.
The boys were familiar with sonar because of the Spindrift work on the Submobile.
He adjusted the sonar pickups, turned the amplifier to maximum, and listened intently.
It was given to drink jardar magn svalkaldr sr and Sonar dreyri.
He listened for code on the sonar equipment, but heard only the weird and nameless sea-sounds.
Thus the sonar waves would appear to be striking no obstacle—and no echo would return to the sonarscopes on the search craft!
An invisible sub—one that sonar pulses would seem to pass right through, as if nothing were there!
It would consist of attaching hundreds of mikes and speakers all over the hull to pick up and transmit the sonar pulses.