The AN/WQX-2 is a diver detection sonar used in defense against swimmer incursions. It is in service with the US Navy. It uses Kongsberg Mesotech components. It can detect divers up to away.
The AN/WQX-2 finds range and bearing of the detected target relative to the sonar. The C3D console developed by SPAWAR converts this to a GPS position. It has software to distinguish diver echoes from shoals of fish, marine mammals, debris, bubbles from boat wakes, etc.
External links
Non-Lethal Swimmer Neutralization Study (about 3 megabytes)(page 3) National Defense Industrial Association: .ppt presentation of 42 slides, 11 MB: look for "SDS". C R&T Waterfront Physical Security Update info for ditto Coast Guard’s Underwater Port Security (archive)