What is a sonobuoy used for?

• A. To detect submarines by passive listening or active sonar when deployed in the water.
• B. To provide GPS navigation data.
• C. To measure atmospheric pressure at sea surface.
• D. To deliver depth charges.

Answer: (A)

A sonobuoy is an underwater sensor used in anti-submarine operations. When deployed, it can listen passively for submarine sounds such as engine and propeller noise, or it can emit a short sonar ping and listen for echoes to detect and help locate a submerged submarine. This dual capability—passive listening and active sonar—makes it a primary tool for detecting submarines from aircraft or ships.

Other options describe functions not performed by a sonobuoy: GPS data is handled by navigation systems, not the buoy's normal role; measuring atmospheric pressure is something a weather or surface buoy would do; delivering depth charges is a weapon deployment action, not what a sonobuoy does.