Firstly, the bomb needs to detonate at the correct depth, so that it can take full advantage of the deep sound channel.
The sofar bomb has to sink fast enough so that it reaches the required depth within a reasonable amount of time (usually about 5 minutes).
[2] To determine the position of a sofar bomb that has been detonated, three or more naval stations combine their reports of when they received the signal.
Dr. Maurice Ewing, a pioneer of oceanography and geophysics, first suggested putting small hollow metal spheres in pilots' emergency kits during World War II.
The spheres would implode when they sank to the sofar channel, acting as a secret homing beacon to be received by microphones on coastlines that could pinpoint downed pilots' positions.