On a barge in lake mead, in Nevada, under a scorching sun, Dave Conlin pulled on long underwear, wool socks and a fleece jacket and pants. He donned an insulated drysuit over all that, strapped two scuba tanks to his back and slung another under one arm. It was so much gear—weighing nearly 200 pounds—that he needed help standing up. His boyish face compressed in a thick neoprene dive hood, Conlin duck-walked to the edge of the barge and stepped into the water.

Plunging in after Conlin, who is an underwater archaeologist with the National Park Service's Submerged Resources Center (SRC), were fellow archaeologist Matt Russell and photographer Brett Seymour, both with the SRC, and Jeff Bozanic, a technical diver under contract to the National Park Service. Bobbing at the surface, the four double-checked their gear and descended into the darkness in a trail of bubbles.

One hundred seventy feet below lay the wreckage of a B-29 bomber. It crashed in 1948 while on a top-secret mission to test components for a missile-guidance system. After World War II, this B-29, known by its serial number, 45-21847, had been stripped of its armaments and fitted with a Sun Tracker, an experimental sensor unit that, when perfected, would allow missiles to navigate by the sun. The cold war was heating up, and the U.S. military wanted missiles that could not be jammed from the ground, as the radar- and radio-guided missiles of the time could be. The Sun Tracker was a precursor to the systems that guide today's cruise missiles.

On July 21, 1948, the bomber took off from Inyokern, California, with a crew of five and climbed to 30,000 feet over the desert, where civilian scientist John Simeroth took measurements of solar radiation to calibrate the Sun Tracker. The plane was making a low pass over the dead-calm surface of Lake Mead when it struck the water at 230 miles per hour, ripping off three engines and setting fire to the fourth. (Pilot error was later found to be the cause.) The plane skipped like a stone, but the pilot, Capt. Robert Madison, put it down safely. The crew escaped into life rafts and were rescued later that day; the worst injury was Sgt. Frank Rico’s broken arm.

In 2001, a private dive team searching for the B-29 using sidescan sonar found the wreck in the northern arm of Lake Mead. Because the bomber lies inside a National Recreation Area, responsibility for the site fell to the National Park Service. The SRC has been surveying the site and preparing it for amateur divers willing to brave the frigid depths for a glimpse of a cold war relic.

As Conlin later described it, a quick descent took them to the plane, which rests right side up, its nose cowling crushed and its back broken, but otherwise in remarkably good condition. Its aluminum skin, lit by powerful dive lights suspended from the barge, shone faintly in the greenish murk. Rectangular holes in the tail show where the fabric coverings were torn away.

The research team sets to work, with Seymour shooting video of Russell to use in an orientation film for visiting divers. Bozanic and Conlin attached tape measures to the plane, from wingtip to wingtip and from the top of the fuselage to where it disappeared into the muddy lake bottom. The operators of a small ROV (Remotely Operated Vehicle) fitted with an electrochemical probe and a video feed will use the measuring tapes as a reference as they guide the ROV around the wreck. They will take readings every foot to measure how much the bomber's surface is corroding in the water.

From one of the bomber's engine enclosures hangs another probe, installed on an earlier dive, that collects data every five minutes, including temperature, salinity and the amount of dissolved oxygen in the water. "This all tells us something about the corrosive environment," says Russell. The team is also documenting the plane’s current condition. "We're establishing a base line so that we can come back in two, five or ten years and see what the visitor impact has been."

The Lake Mead bomber is believed to be the only submerged B-29 in the continental United States, and the park service predicts it'll become a popular dive site. SRC divers have already mapped the B-29 and also installed mooring buoys nearby to keep dive boats from dropping anchors onto the bomber. Cables run from the buoys to a weight next to the plane to guide divers through the dark water.

"It will be a once-in-a-lifetime dive," says Bill Gornet, owner of Dive Las Vegas. "You really don’t know how big a B-29 is until you’re on top of one—it's monstrous." With a wingspan of 141 feet and a tail that stands 29 feet high, the B-29 was the heaviest, most advanced bomber of its time. The Lake Mead plane, with its guns and armor removed, closely resembled a more famous pair of bombers that were stripped down for speed: the Enola Gay and the Bockscar, which dropped atomic bombs on Hiroshima and Nagasaki, respectively. Fewer than a dozen B-29s are on display at museums and air parks around the country, including the Enola Gay at the Smithsonian Institution's Steven F. Udvar-Hazy Center near Washington Dulles International Airport and the Bockscar at the United States Air Force Museum at Wright-Patterson Air Force Base in Ohio.

Although diving on a WWII bomber is a far cry from dusting off 1,000-year-old clay pots, it's still archaeology. Few scholars combine technical diving skills with the archaeological experience of the SRC. Based in Santa Fe, New Mexico, the squad's five experts dive on locations around the world. If an artifact is underwater and in a national park, the SRC usually gets the call. They've had a hand in raising a sunken Civil War submarine, and now, says the squad's chief, Larry Murphy, the group is surveying the USS Arizona in Pearl Harbor and a sunken ferry off New York's Ellis Island. "The first question is what's there, and the second question is what's happening to it."

Conlin, 40, says he has wanted to be an underwater archaeologist since childhood, when he watched Jacques Cousteau films and National Geographic documentaries about Mediterranean shipwrecks. "Growing up in Colorado, I didn't even see the ocean until I was 6," he says, "but I've known I wanted to be down there finding amazing stuff for a long time."

Deep underwater, time is precious, and there's little room for error. Below 130 feet, SRC divers breathe special air mixes of helium and oxygen, and must abide carefully by timetables telling how long they can safely stay at a given depth—to the minute—or they risk decompression sickness (the bends). The B-29 archaeologists can spend only two hours underwater, and they must use three-quarters of that time returning to the surface in stages. That leaves only half an hour on the bottom. And every fourth day is a rest day, giving each archaeologist at most only three hours of hands-on time a week.

Two hours after Conlin and co-workers jumped into the lake, they surface, right on schedule. Conlin is shivering—some of the 48-degree Fahrenheit water seeped through the neck of his suit—but otherwise everything went perfectly. That night, barefoot on a houseboat tucked into a secluded cove, the divers revise the detailed drawings of the plane they made in 2003, go over the day's photos and video, and plan the next day's dive.

"The first time you go down it's spooky," says Bozanic, who has decades of diving experience in caves around the world. "The deeper you go, the darker and colder it gets. Everything is covered in silt, there's no point of reference. Then the plane looms out of the gloom. It's downright scary."

SRC divers work for the thrill of discovery and the chance to challenge themselves in one of the planet's most unforgiving environments. "Your focus," Russell says, "is split between archaeology and staying alive."