sonobuoy
noun
so·no·buoy ˈsä-nə-ˌbȯi 
-ˌbü-ē
: a buoy equipped for detecting underwater sounds and transmitting them by radio
Example Sentences
Recent Examples on the Web Next, the sonobuoy unfolds a five-sided array of 40 underwater microphones (known as hydrophones), creating an underwater listening post. 
Kyle Mizokami, Popular Mechanics, 6 Jan. 2022 In addition the Trackers were armed with sonobuoys, droppable listening posts that radio any contacts back to the plane. sandiegouniontribune.com, 13 May 2018
Kyle Mizokami, Popular Mechanics, 6 Jan. 2022 In addition the Trackers were armed with sonobuoys, droppable listening posts that radio any contacts back to the plane. sandiegouniontribune.com, 13 May 2018 Word History
First Known Use
1937, in the meaning defined above