MIL-S-81478C, MILITARY SPECIFICATION: SONOBUOY AN/SSQ-57A (01 APR 1985) [NO S/S DOCUMENT]., This specification establishes the design, performance, and acceptance requirements for the AN/SSQ-57A Sonobuoy herein referred to as the sonobuoy. The sonobuoy relays, by FM VHF radio transmission, sounds in the audio frequency range initially received by a cable-suspended drophone system. The sonobuoy is an aircraft launched, expendable floating device, intended for the purpose of detecting underwater acoustical energy radiated bysubmarines.