Free diving is similar to racing in that there is a lot of equipment involved, and everything has to be used in precisely the right way. When he's diving, Hunter-Reay rocks Riffe blades, elongated fins that are at their most effective when kicked slowly and steadily. At first, Hunter-Reay tried hard to get down too fast, but he realized he was paying a price.

"Free diving is all about efficiency, which makes it just like racing," says Hunter-Reay. "If you get tense or anxious, you pay for it with oxygen, so you have to be mindful of that." The driver says it took him a while to learn how to move underwater and to arrive at thinking of air as fuel that he needed to keep in the tank. Now he does everything smoothly in order to wring the maximum mileage out of each dive.