Swimfin
Swimfins, swim fins, fins or flippers are finlike rubber or plastic shoes worn over the foot to help movement through the water in water sports activities such as bodyboarding, bodysurfing, kneeboarding, swimming, and various types of diving.
Scuba divers use fins to move through water better, as human feet provide poor thrust, especially when the diver is carrying equipment that increases drag in the water. Very long fins and monofins are used by freedivers in the search for underwater propulsion that does not require high frequency leg movements.
Swimfins are also known as flippers outside of North America.
Some people call them "flippers" in North America and elsewhere, because the word "fin" can also mean the fins on cars and auxiliary airfoils on tails of aircraft, which are parallel to the fluid flow. The comic book character Aquaman has had this sort of fin on the calves of his boots.
Benjamin Franklin made a pair of early swimfins while he was a young boy living in Boston, Massachusetts near the river; they were two thin pieces of wood, about the shape of an art palette, which let him move faster than he usually did in the water.
Other early inventors including Leonardo da Vinci had toyed with the concept of swimfins.
Louis de Corlieu in France and Owen Churchill in the United States, working independently of each other, were the first to make swimfins a practical reality. Churchill's design caught the attention of the US Navy, which wanted to issue it to their underwater demolition teams in the early 1940s; and fins of his design can still be found in just about any sporting goods store or surf shop.
Different types of fins eventually evolved to address the unique requirements of each community using them. Scuba divers, in particular, need large wide fins to enable them to overcome the water resistance caused by their diving equipment; snorkelers need lightweight flexible fins; ocean swimmers, bodysurfers, and lifeguards favor designs that stay on their feet when moving through large surf.
Some fins have a water vent through the blade, opening backwards on the underside and forwards on the upper side, as in the third image. As the hip joint is flexed, a jet of water blows backwards out of the vent in the fin. This type of fin is sometimes called a "jetfin"; but the name "Jetfin" is correctly a tradename.
For similar reasons some swimfins have the end of the blade split; this feature may have been copied from fishes' tails.
See also: monofin
Trivia
Owen Churchill, already a wealthy man, became a multi-millionaire from his "invention" of the first popular swim fin, which gained in use in the late 1930s and early 1940s. The income from his then-patented and now-commonplace device let him pursue his passion of competitive sailing. Churchill became the primary patron and team captain of the United States Olympic Yachting team at both the1932 (Los Angeles) and 1936 (Berlin) Olympic Games. Churchill was also a lifetime member of the Los Angeles Yacht Club, where memorabilia of his exploits is on display to this day. During the 1984 Olympic Games in Los Angeles, special recognition was given to Churchill by Peter Ueberroth for his lifelong efforts to promote sailing. Churchill's Star Fleet yacht, The Angelita, was fully restored for the occasion and re-christened at the time in Los Angeles harbor.