More and more, scientists are looking to nature to inspire efficient design. Take the engineers at DaimlerChrysler, for example, who built a more aerodynamic car modeled after the tropical boxfish. (It's still a concept car.)
Now, researchers at the Massachusetts Institute of Technology are taking cues from the bluegill sunfish to build a mechanical fin that could one day be used on a more advanced robotic submarine, or autonomous underwater vehicle (AUV). They're modeling the bluegill sunfish because it has a distinctive style of motion that involves a constant forward thrust with no backward drag, unlike a human swimming the breaststroke, for example.

By mimicking this forward motion, MIT scientists hope to build a more agile mechanical fin that could power a propeller-less AUV that could perform military tasks, such as sweeping mines or inspecting harbors. (Current AUVs can map the ocean floor or survey shipwrecks.)
"If we could produce AUVs that can hover and turn and store energy and do all the things a fish does, they'll be much better than the remotely operated vehicles we have now," James Tangorra, an MIT postdoctoral associate working on the project, said in a statement.
The researchers are still experimenting with how best to mirror the efficiency of the sunfish fin and built a mechanical fin with the right materials. But early tests of a prototype built with an electricity-conducting polymer have proved successful.