The locomotion of swimming animals can be easily observed in recent forms. Nevertheless, even today, there are still considerable uncertainties regarding the exact mechanism of movement. Ideas about the locomotion of vertebrates and especially of fish go back in part to the 19th century. Wrong views were never recognized and have been accepted without criticism until today. For example, it is repeatedly claimed that the caudal fin in fish, especially in large ones such as tuna, lamnid sharks and whales, or in fossil reptiles such as ichthyosaurs, produced the propulsion. It may look like the tail fin drove the animal, but in fact, it is quite different. The caudal fin is not involved in propulsion at all! The video of successful thrust by a simplified artificial fish body further down can serve as an unquestionable proof. In reality, the thrust is caused by the alternating curvature of the trunk and the resulting forced flow around the body. More details on the following page. Various amateurish efforts to research, imitate and technically exploit fish propulsion on a false basis have therefore all failed miserably so far, despite the actors’ full-bodied expectations of success.