Humans are terrible swimmers

Humans are terrible swimmers, converting roughly 3 percent of their kicks, strokes and general underwater exertions into forward motion. We can boost our efficiency to 10 percent by adding fins, but dolphins, by comparison, can turn 80 percent of their energy into thrust. Not to be outdone, the Pentagon’s research wing, DARPA, is developing a contraption that lets Navy SEALs and other combat divers swim faster, and with less effort.

Instead of kicking, PowerSwim calls for a kind of undulation as its hinged foils pivot up and down. Similar to the way a dolphin or tortoise pumps its fins, this motion generates both lift and thrust. And while artificial fins operate within the swimmer’s own wake (they form a kind of expanding cone, starting at a swimmer’s shoulders), the PowerSwim’s lead foil—or propulsor foil—sweeps through the water just outside that wake.

When used properly, the device allows swimmers to cover a given distance up to 150 percent faster than with fins, while using the same amount of energy...[Popular Mechanics]