Towed acoustic hydrophone arrays having any of the following: (a) Hydrophone group spacing of less than 12,5 m or ‘able to be modified’ to have hydrophone group spacing of less than 12,5 m; (b) Designed or ‘able to be modified’ to operate at depths exceeding 35 m; (c) Heading sensors specified in VII.A6.003 (d) Longitudinally reinforced array hoses; (e) An assembled array of less than 40 mm in diameter; (f) Hydrophone characteristics specified in (a) above or a hydrophone with a hydrophone sensitivity better than 180 dB at any depth with no acceleration, or (g) Accelerometer-based hydro-acoustic with the following: 1. Composed of three accelerometers arranged along three distinct axes; 2. Having an overall ‘acceleration sensitivity’ better than 48 dB (reference 1 000 mV rms per 1g); 3. Designed to operate at depths greater than 35 metres; and 4. Operating frequency below 20 kHz.