posted 06-05-2013 01:53 PM               

Acoustic pulses, particularly sound at low frequencies i.e. less than a few hundred Hz, are conducted very efficiently and can travel great distances in the ocean if they are trapped in this acoustic "wave guide" channel. This principle is exploited by submariners and marine animals.

During World War II Dr. Maurice Ewing, a pioneer of oceanography and geophysics, suggested that dropping into the ocean a small metal sphere (called a SOFAR bomb or SOFAR disc), specifically designed to implode in the depths of the SOFAR channel, could be used as a secret distress signal by downed allied pilots. A position could be determined from the differences in signal arrival times at receiving stations with known geographic locations.

posted 06-05-2013 03:22 PM               

Originally posted by CNewport 01-21-2006:

"SOFAR stands for Sound Fixing and Ranging; they were small explosive devices attached to the Mercury spacecraft to indicate the splashdown location. They did this by detonating at a specific water depth in what was called "the SOFAR listening channel" which acted like a waveguide allowing the sound to be heard for long distances, possibly several thousand miles if I remember correctly.

Each device was both armed and detonated by water pressure and contained 11 ounces of HBX, a military explosive similar to TNT. The device attached to Liberty Bell 7 was located and removed by UXB International and fortunately was a dud.

From what I recall, about 10% of these devices did not explode. I find it especially ironic that the one capsule that did sink to a "nonrecoverable depth" had a SOFAR bomb that was a dud. If it had gone off, it would not have destroyed the capsule; however, it certainly would have made a mess of things."