Abstract: The underwater signalling and identification device comprises an emitter (5) having four submerged transducers (10 to 13) arranged to form a square and fitted in a water-tight case (25) placed above an opening (7) formed in the hull of a ship, and also comprises a transducer-control circuit designed to emit an identification signal specific to the vessel and made up of a series of figures or letters in Morse code, the signal being emitted at at least one frequency selected as a function of the sound spectrum of the vessel and falling within the range of 4 to 6 kHz, the strength of emission of the signal being in accordance with the relationshipLI.sub.sl .gtoreq.LI.sub.bl +.DELTA.(dB),wherein LI.sub.sl is the level of acoustic intensity converted to the unit of distance of the identification signal of mean frequency f.sub.s.