Ronnie Simpson ambles up from the docks of the Stockton Sailing Club. At 25, he is whip thin and browned by the Northern California sun. His hair is close-cropped, and he's wearing his preferred uniform: boardshorts and a faded sailing T-shirt. He's in Stockton to take possession of a 28-foot Albin Cumulus sailboat that he just bought for $2,800, with money borrowed from a friend. The boat is called Chippewa, and the cockpit is strewn with tools, gear, and empty beer cans. A dark scrim of weeds encrusts the bottom, but beneath the grime you can see the shape of a blue-water pedigree. Ronnie is taking Chippewa down the San Joaquin River to San Francisco Bay, to the Marina Village Yacht Harbor, in Alameda, where the boat will become his new home. As soon as he feels it's ready to sail to Hawaii and beyond, Ronnie Simpson will do what he does best: take off and see what happens.

Ronnie looks like any boat bum who works odd jobs on the waterfront. He's always up for a party or a deal on Craigslist, and he's not averse to drinking beer within an hour or two of a late breakfast. He has a laid-back, renegade charm and tells stories as easily as he draws breath. He makes friends wherever he goes, and sometimes it's hard to keep track of all the girlfriends ("she was soooooo hot") who've wandered into his life. It wasn't very long ago that he had just $15 to his name.

But Ronnie is not an aimless vagabond. To understand this, you need to take note of the long, moon-shaped scar under his left arm, which arcs around his rib cage from pectoral to scapula. You need to observe the seven-inch vertical scar that bisects his stomach, deviating only slightly around his belly button. You should also take in the coin-size cicatrices that pepper his torso, pale blotches against the dark of his skin, and try to imagine the searing heat that branded him. Ronnie served as a marine in Iraq, and on the night of June 30, 2004, at age 19, he almost died.

How he got from there to here is a wrenching story, of how war takes human beings, breaks them into little pieces, and gives them two choices: surrender or fight. Unlike many veterans, Ronnie eventually found a way back from his life-threatening injuries, enduring a long hospitalization, the death of his father, and a few years of soul-numbing suburban striving before the accidental discovery of sailing and adventure helped him to reinvent himself. It was an odyssey that almost killed him more than once, but in the end, it also saved him. "I have never been so broke in my life," he says. "And I've never been happier."

After a night of ale-assisted slumber in Chippewa's simple cabin, we ease the boat out of the slip as soon as there's enough light to navigate the marina fairway. From Stockton, we've got some 50 miles of motoring down the channels of the San Joaquin River before we're released into San Pablo Bay, and San Francisco Bay beyond. Apart from trying to avoid getting lost in the maze of side channels, pulling weeds off the prop, and wishing there were enough wind to sail, there's not much else to do besides hear the tale of Ronnie Simpson's resurrection.

RONNIE DOESN'T ACTUALLY remember the moment his life was blown apart. He was in a Humvee, bouncing down Highway 11 between Baghdad and Fallujah. The cooling night air was thick with dust and diesel exhaust, and the hard heft of a tripod-mounted 50-caliber machine gun was in his hands. Highway 11 was not a great place to be at 11:30 p.m. on June 30. The Sunni insurgency was in full metastasis, and the radio in the Humvee was chattering with reports of units getting hit all across the country.

Ronnie's platoon, part of the 2nd Battalion, 2nd Marines, was helping escort a convoy of Army trucks back to its base. Ronnie was standing in the Humvee's truck bed as they followed a large Army transport. He saw a single muzzle flash flare in the darkness, then another. A fusillade of shots ripped into the convoy, and then a firefight erupted hot and heavy. Ronnie swiveled the 50-cal toward the enemy position and started firing.

The Army truck in front ground to a halt. "Why are we stopping? Why are we stopping?" Ronnie shouted. "Well, the fucking Army stopped," his commander snapped back. No one knows for sure what happened next. There was a whoosh that sounded like a rocket-propelled grenade, then a white-hot explosion. All Ronnie knows is that the world went black.