Autonomous vehicles cooperating across various ocean depths will be useful for real time hydrography and to characterize acoustic propagation - a critical factor in antisubmarine warfare. Mine countermeasures is another obvious mission, along with autonomous swarmed attack against surface or sub-surface platforms.
Research being conducted by CcCoRo - here, one AUV detects an object and invites others to join it:
Ah, the possibilities. A lot of problems in the inshore areas might be addressed using this concept.