of the main tube housing 41 passes through the projected center point of the tetrahedron of hydrophones this central axis is also the axis of the direction of travel of the whole unit there are three hydrophone tubes 42 43 44 arrayed around the main tube housing 41 with 120 degrees separation of one tube to the others and located at 60 degrees 180 degrees and 300 degrees around the central axis of the main tube housing 41 the three hydrophone tubes are the fore and aft hydrophone tube 42 located at 180 degrees or directly below the main tube housing in use the port hydrophone tube 43 and the starboard hydrophone tube 44 are located at 60 degrees and 300 degrees the central axis of the main tube housing 41 passes through the projected center point of the tetrahedron of hydrophones with the consequence that the fore and aft hydrophones 1 4 and the center point are in a plane along the central axis and the port and starboard hydrophones 2 3 and the center point are in a plane perpendicular to the central axis the distance between the central axis of the main tube housing 41 and the central axis of the fore and aft hydrophone tube 42 is therefore one fifth shorter or 80 of the corresponding distance for the port and starboard hydrophone tubes 43 44 the fore structure 20 functions as fairing and stabilization of the mid structure 40 and is attached in smooth continuations of.