Swim like a dolphin with Powerswim
DEKA has made the Powerswim device for DARPA. Normal swim fins are inefficient as they only convert about 10% of the energy to propulsion. The Department of Defense requirement was to increase the speed compared to normal swim fins by 50% and reduce by a factor of two the energy needed to maintain a speed of 1 knot. The project has been a success as the the swimmers can sustain speeds of more than 2 knots increasing energy efficiency from 10% to 85%!
The result reminds me of the SeaBreacher with a front wing and an oscillating foil:
Powerswim has been made for the DoD but I am sure it will arrive on the commercial market sooner or later.