sonobuoy

thumb|right|300px|Sonobuoy being loaded onto a USN P-3C Orion aircraft thumb|Hand deployment of a sonobuoy in the Arctic Ocean from the aft deck of the R/V Sikuliaq

A sonobuoy (a portmanteau of sonar and buoy) is a small expendable sonar buoy dropped from aircraft or ships for anti-submarine warfare or underwater acoustic research. Sonobuoys are typically around in diameter and long. When floating on the water, sonobuoys have both a radio transmitter above the surface and hydrophone sensors underwater. Sonobuoys are mission-critical platforms for enhancing Undersea Domain Awareness (UDA), providing an effective means to detect, locate, and track submarines and other underwater threats. Playing a key role in anti-submarine warfare (ASW) and other naval operations, they support in maintaining naval security and in protecting naval carrier strike groups.