The U.S. Navy together with General Atomics last November tested the MQ-9A Block V Reaper UAV, which is planned to be used for submarine detection.
In particular, tests included dropping of hydroacoustic devices for detection of enemy underwater objects using UAVs. This is written in Defense News.
In the framework of exercises, the drone tried to track the target, which imitated a submarine. For this purpose, the UAV dropped about 10 hydroacoustic devices, the data from which was then collected and transmitted to the center for control.
The tests are part of a project to develop the MQ-9B SeaGuardian maritime drone, which could replace anti-submarine assets such as the P-8A Poseidon aircraft and reduce the cost of defense against underwater targets.