a cylinder of carbon fibre with titanium caps at either end, that is metal will stop so maybe you tap on the uthappa at regular intervals, timed intervals, and you do it with a pattern, 0k. timed intervals, and you do it with a pattern, ok. you do that to distinguish the noise from the general din of the ocean. so when they are listening, because they are because they have these various sonobuoys on the surface, when they are listening they think that is not are listening they think that is not a ship s propeller around here, that is not us, that is not our noise, it is not us, that is not our noise, it is completely different and it is not whales, they don t make that noise, and it is not submarines. you can then use that sound to try and get a fix on the location. 50 if you have a number of different sonobuoys on the surface, if you time the arrival of that pattern of sound coming to those different sonobuoys then you can geo locate, much like gps, you have different satellites, sen