Wiktionary
n. (context nautical military English) A buoy that sends a radio signal when it detects the sound of underwater objects (such as submarines)
Wikipedia
A sonobuoy (a portmanteau of sonar and buoy) is a relatively small buoy (typically , in diameter and long) expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater acoustic research.
Usage examples of "sonobuoy".
Murphy could feel the vibrations from his feet as the main engines aft began to accelerate them through the water of the shallow bay, moving them away from the sonobuoys.
Four helicopters were dropping sonobuoys in hope of reacquiring it, and a half-dozen sonars were pinging away, but so far it looked as though the submarine had evaded the angry escorts.
Besides, the antisubmarine aircraft had deployed enough sonobuoys to constitute a hazard to navigation.
A sonobuoy dropped ten minutes earlier had detected a weak signal, held it for two minutes, then lost it.
As he gave orders to his crew chief to release the sonobuoys along a line his copilot had devised, he watched the cruiser Gridley's close-in weapon system bring down a missile bearing down on her with a shower of rapid fire 20-mm.
On detecting something, a sonobuoy reported to its mother aircraft and then automatically sank lest it fall into unfriendly hands.
It hadn't taken the enemy long to begin the hunt, using sonobuoys to send out pings of sound that had echoed through the sub's steel hull.
Penguin 8 carried eighty sonobuoys, four Mk-46 ASW torpedoes, and some other high-technology weapons-none of which were of the least use against a simple large target like this merchie.
The Orion carried over fifty sonobuoys, and was soon dropping them in sets both above and below the layer.
The suddenly increased noise of her cavitating screws was discernible to several sonobuoys and Pharris's tactical sonar.
Confused by many brief reports from sonobuoys, most of which were probably false signals to begin with, the computer-generated estimate for the submarine's position covered over a hundred square miles.
If the Soviets were deploying their sonobuoys in angled lines left and right of the formation, that could mean that their ships were heading right for Chicago.
Chicago ran for twenty minutes, zigzagging slightly to avoid the Russian sonobuoys, as the firecontrol men kept updating their solutions.
Then he would have to depend on sonobuoys alone, and Morris trusted his towed sonar more than the buoys.
Their helicopters had laid a string of sonobuoys, and their ESM radar receivers listened for the pulsing signal of a Soviet-made radar.