OVERVIEW: Expendable acoustic sensors deployed by naval aircraft or ships to detect and monitor underwater sounds from submarines, ships, and marine life. They provide wide-area surveillance by passively listening for acoustic signatures without emitting any signals.

GENERAL DESCRIPTION: Passive Non-Directional Sonobuoys operate by detecting underwater acoustic energy across broad frequency ranges and transmitting the collected data via radio to monitoring platforms. These sonobuoys do not have directional capability, meaning they capture ambient underwater noise from all directions. They are primarily used in anti-submarine warfare (ASW) for early detection and tracking of underwater contacts. Typically deployed in patterns to cover large ocean areas, these sonobuoys complement active sonar systems and other acoustic sensors. Their simple design allows for cost-effective, rapid deployment in both shallow and deep waters. Frequency reception depends on variant but generally covers low to mid-frequency bands suited to detect submarine propulsion and ambient ocean noise.

ROLE SUMMARY:
Category: Acoustic Surveillance
Primary Use: Passive detection and monitoring of underwater contacts
Function: Receive and relay acoustic data to ASW platforms
Platform: Deployed from maritime patrol aircraft, helicopters, surface ships, and submarines

See Specific information under [Sensors/EW] section.

SOURCE:
NATO Standardization Agreements (STANAGs)
Naval Technology Online: https://www.naval-technology.com/projects/sonobuoys/