https://www.popularmechanics.com/military/weapons/a34451548/navys-new-hammerhead-mine/
Extract：
“Here’s how Hammerhead works. After the XLUUV releases the Hammerhead, the mooring module anchors the mine to the seabed where it might wait days, weeks, or even months for the activation order. Once the command and control module receives the activation order, the sensor module quietly listens for the acoustic signature of approaching enemy submarines, running suspected underwater noises through the signal processing and decision module and comparing them to the recorded signatures of known enemy submarines. If an enemy sub is confirmed present, Hammerhead can release its Mk. 54 torpedo and then signal its controllers it has engaged an enemy sub.”
