Wired has an article about the Navy using robots to sweep for mines. The article talks about some of the Navy's possible choices, which are: the ARIES that has a camera to look for mines, the CETUS that hovers over the water to look for mines, and the BPAUV that has side-scan capabilties to image mines with sonar.

Here's a nice page on some of the Autonomous Underwater Vehicle Resources.

You can read about an older Robots.net article here.