This is a detailed, textured model of a sonobuoy (sonar buoy).
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, while one or more hydrophone sensors and stabilizing equipment descend below the surface to a depth that is (preset) variable depending on environmental conditions and the search pattern. The buoy relays acoustic information from its hydrophone(s) via UHF/VHF radio to operators onboard the aircraft. (courtesy wiki)