Sam Fisher- OmegaO Swimming

 Working under the headlamp's beam, Fisher unzipped the backpack and pulled out a black aluminum cylinder the size of a Pringles potato chip canister. Modeled on the commercial version known as Spare Air, this DARPA-modified miniature scuba tank had been named OmegaO by some long-forgotten techno-geek with a dark sense of humor. Omega for "last," and O, the symbol for oxygen--the last breath you're likely to take. Despite its diminutive size, the OmegaO was something of a marvel, able to hold 2.5 cubic feet, or 70 liters, of air, which translated into roughly forty-five to fifty lungfuls. For an experienced diver this could mean as much as five or six minutes underwater, enough for a strong swimmer to cover a quarter mile or more. Fisher was a strong swimmer.
...

  With a grating jolt, the BMW hit the riverbed; the car continued to slide for another ten feet until the tires sunk into the mud, bringing it to a halt. He could feel the current buffeting the sides. Water bubbled up to his chin. He got to his knees and, head pressed into the ceiling, donned his backpack. He put on the regulator and punched the button to test the airflow and was rewarded with a short hiss. He took a breath; the air was cool and metallic tasting. He closed his eyes and the water enveloped him.

  Silence.

  He sat still for a moment and listened to the ticks and pings of debris washing over the BMW, then opened his eyes. His headlamp beam was a cone of white before him. He checked the windows but saw only darkness and occasional bits of swirling sediment and plant matter. In which direction had the car settled? He pressed his hand first against the passenger-side window, then the driver's side; here he felt more pressure against the glass. He scooted back to the other side, lifted the handle, and put his shoulder to the door. It burst open. Fisher tumbled out and landed on his side, buried up to his collarbone in mud. Loosened by the impact, his headlamp slipped off his head and slipped away. He snagged it, settled the straps back on his head, and cinched them down.

  He started swimming.

  THE current, combined with his paddling, doubled his submerged speed. With his vision narrowed to what the cone of light from his headlamp illuminated, he had the sensation one got on an airport's moving walkway. With no fixed references to latch on to, his brain was telling him he was swimming at a normal pace, but his body knew otherwise. Counting seconds in his head, Fisher swam hard for a minute, then turned left on the diagonal, aiming for the Rhine's western shore. After another two minutes he felt the current suddenly slacken, and he knew he was clear of the main channel. He felt something soft slide over his chest and belly, and it took him a moment to realize it was mud. The bottom was rising. Twenty feet, he estimated. He was perhaps thirty feet from the bank. He had no fixed plan, but knew he needed to surface close to land, close to cover, lest he be spotted by rescue boats or an onlooker.

  The current changed again and he felt his body spiraling left into some kind of vortex. His kicking feet touched mud, and then the water was calm again. He angled upward. The light increased. The surface came into view. Using his hands like flippers, he backpedaled in the water, slowing down until he was hovering a few feet below the surface. Directly ahead he could see trees: fuzzy broccoli shapes silhouetted against the sky. There was a gap between them. An inlet. He turned over, dove to the bottom, and swam on, using only his feet, arms spread wide, until he felt his fingers trailing over soil walls. The inlet continued to narrow and bottom out until his chest was scraping the bottom. He rolled onto his back and used his heels to wriggle forward until his head broke the surface. He blinked his eyes clear and found himself staring at tree branches, so close he could have reached out and touched them. He was right: an inlet. Shaped like an elongated V, it was at least two hundred feet deep. At its midpoint was a wooden footbridge. Someone was standing on it. No, two people. A man and a woman with their backs to him--watching the show in the main channel, he assumed. Moving with exaggerated slowness, Fisher reached up and removed the OmegaO's mask.

- Conviction, Chapter 16