Dolphins protecting humans, helping humans and guiding humans has a history that has been documented for over two thousand years.

Dolphins and sharks are enemies, and dolphins do not always win the fight. If they are able to attack the shark and use their noses to butt the underbellies, they hit hard enough to rupture internal organs and the sharks limp off and die. However, if the shark gets first dibs in, the dolphin ain't gonna win. (I am assuming it was bottle-nosed dolphins involved.

They are beautiful, intelligent creatures, and I think it was a Dr Liddy (?) in 1967 who did great research into their ultrasonic communication.