Modern methods for employing under‐water sound as an aid to navigation are based upon the binaural sense.The earliest devices, exemplified by the “C” tube, etc., mechanically placed the ears of the observer on the extremities of a beam to be rotated in a horizontal plane beneath the sea. Such cumbersome equipment was improved by employing fixed under‐water receivers in conjunction with an adjustable compensator for obtaining a binaural balance.Electrical lag lines have replaced acoustical tubes for obtaining the necessary time lag to affect compensation. The effectiveness of such a two‐spot system is hampered whenever more than one sound source is present. This difficulty was subsequently overcome by obtaining a directional sensitivity by means of a multi‐spot system which compensates simultaneously for a binaural and maximum focus.Observations upon the compensators may likewise be made upon sounds traveling in a vertical plane. This enables continuous depth soundings to be taken with the vessel under way at full speed, a valuable feature.Apparatus has also been perfected for acoustic depth soundings by timing the echo of sound reflected from the sea bottom. The use of super‐audible sound waves, which can be projected in a slightly diverging beam, offer great possibilities for the location of icebergs, etc.