A sonobuoy (a portmanteau of sonar and buoy) is a relatively small (typically 4⅞ inches, or 124 mm, in diameter and 36 inches, or 910 mm, long) expendable sonar system that's dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater acoustic research. Theory of operation The buoys are ejected from aircraft in canisters and deploy upon water impact. An inflatable surface float with a radio transmitter remains on the surface for communication with the aircraft,… (More on Sonobuoy)