Photos: This boat swims like a dolphin

Unlike a submarine, the Dolphin doesn't use ballast in order to sink into the water. Rather, it "uses its forward momentum and variable pitch-diving planes to fly beneath the surface.

The distinction is much like the difference between an airship (which uses a lightweight gas to obtain lift) and an airplane (which uses its wings to achieve flight)," the Innespace site says.

In the event of an emergency, the design also forces the craft to the surface in an upright position.

Photo by Innespace