All four classes of unmanned surface vessels
Table of missions
Smallest X class USV for recon mainly
Harbor class specifications, 7 meters long, Zodiacs with weapons, can defend against attacks like the one on the USS Cole
Snorkler class, 7 meter submarine, stay in the water for 1 day
Fleet class USV, 11 meters long, good speed and able to stay in the water for 2 days
If costs were held down to $1 to 5 million per USV and UAV, then it would make sense to spend 10%-50% of the Navy budget to provide 10-100 USVs and UAVs per manned Navy Vessel. Every manned ship would have the equivalent of an unmanned carrier group. Mini-unmanned carrier groups would be far cheaper than current manned versions.
This is the damage to the USS Cole. A Zodiac with a couple of terrorists and explosives was allowed to get too close to the USS Cole. Robotic Zodiacs could intercept and challenge such craft at a standoff distance from Navy vessels.
Wikipedia has nifo on Autonomous Underwater Vehicles