Vector hydrophones with applications to seabed warfare

Commonly-used hydrophones respond to acoustic pressure but give no bearing information unless used in an array. Vector hydrophones, on the other hand, provide bearings from a single hydrophone regardless of frequency, making them ideal to record aspect-dependent acoustic signatures. How do vector hydrophones work? What can you expect of them? What are their limitations?  Where can they be used? Examples include as a ad hoc bottom mounted sensor to collect data such as narrow band finger printing of targets of opportunity, or as an efficient critical asset monitoring tool and counter seabed-warfare.