Ah, the fleet tuna, master of the open ocean.  This graceful, powerful fish is best known to Americans as an excellent rare steak, a common sandwich filling, or maybe a hazy memory of cartoon pitchmeister, Charlie the Tuna.  Yet the tuna is actually quite a fast and efficient swimmer with a yellowfin once making over 40kts after being caught on a line.

The thought has occurred to people that fish may be worthwhile of study if you're interested in better ways to propel an underwater vehicle such as an AUV.  Back in 1995, designer David Barrett built a robot fish for his PhD thesis.  This was the original RoboTuna named Charlie I and it became the subject for some interesting scientific work - and later a great article in Smithsonian magazine (link below).

Here's a great website on radio controlled (R/C) submarines.
http://www.rc-submarines.com/r_c_subs.htm 

There's a lot of information here and plenty of links to other sites, but I have to include this r/c sub made from plumbing pipe.  It's crude in a well-designed sort of way.  Go to this website http://web.ticino.com/Submarine/ and click on E1 to see what I'm talking about.