Lake Mead hides many sunken treasures in its cold, freshwater depths. Lost in the lake at the dawn of the Cold War, a crashed B-29 Superfortress bomber kept its secrets for nearly 60 years.

Hoover Dam formed the giant, 248-square-mile reservoir in parts of Arizona and Nevada during the 1930s. The lake's size isn't the sole reason why the big bomber remained lost for so long. Another was the highly-classified nature of the flight.

The Overton Arm B-29 — named for the part of Lake Mead where it crashed in 1948 — tested a secret ballistic-missile guidance system. The nature of the test required a risky and dangerous flight.

But a historic drought has lowered Lake Mead's levels, and may soon give recreational divers access to the sunken bomber.

Today, a handful of B-29s still exist, and only one can fly. The two most famous Superfortresses — Enola Gay and Bockscar — dropped the atomic bombs on Japan and now reside at the National Air and Space Museum.

Finding another B-29 is remarkable. Diving to one as a shipwreck is extraordinary.

When introduced into combat in 1944, the Superfortress was one of the largest, most technologically advanced warplanes ever built. It could carry a 10-ton bomb load more than 5,000 miles — at speeds greater than 350 miles per hour.

Its pressurized cabin was a first in an American bomber, and protected its crew from the rigors of the aircraft's 35,000-foot cruising altitude.

The B-29 carried America's new atomic weapons across thousands of miles of ocean. Although rushed into service while its final specifications were still in flux, the Superfortress' basic design was good enough to keep in service through the Korean War.

(U.S. Air Force/Courtesy War Is Boring)

Secret mission

After World War II, the Superfortress took on extra jobs as an aerial refueling, reconnaissance and weather research plane. The B-29 also turned into a high-altitude laboratory for the Air Force's next long-range weapon.

Wernher von Braun and his team of German rocket scientists developed the U.S. Army's ballistic missile program using captured V-2 rockets. But the V-2 had a primitive and inaccurate guidance system. This spurred American military scientists to modify ballistic missiles into precision-strike weapons.

One such project sank a B-29 — serial number 45–21847 — in Lake Mead.

This individual bomber was one of the last Superfortresses built. The U.S. Army Air Forces received it 11 days after Japan surrendered on Sept. 2, 1945. In late 1947, the plane gave up its defensive armament and joined the military's Upper Atmosphere Research Project based at what is now Edwards Air Force Base in Southern California.

On June 21, 1948, the B-29 took off and headed east toward Las Vegas. Its five-man crew prepared a highly-classified device mounted in a clear dorsal dome atop the bomber's fuselage.

The device, known as a "sun-tracker," was a new kind of missile guidance system. There's little publicly known about it, but a 1954 patent application suggests the sun tracker allowed a missile to get its elevation and orientation from sighting the sun. The device came from the Applied Physics Laboratory at Johns Hopkins University.

Testing the sun tracker required the B-29's crew to fly a risky course — repeatedly ascending to 35,000 feet before plunging to 100 feet above Lake Mead's surface.

But the lake was dead calm, and its surface reflected the sun like a mirror. As the big bomber skimmed the water, Capt. Robert Madison lost his depth perception and crashed into the lake at 230 miles per hour.

The impact tore off three of the giant plane's engines. The bomber skipped across the water like a huge metal bird, before it stopped and sank into the Overton Arm of the lake. The crew had time to escape in life rafts, where they waited several hours before National Park Service employees rescued them.

At the time, there were still plenty of B-29s, and the mission's secrecy may have discouraged active searches. But as time passed and Superfortresses became rare, aviation enthusiasts recalled the lost bomber.

(National Park Service Illustration/Courtesy War Is Boring)

Sunken wreck

When ambitious wreck hunters located the plane without permission in 2001, the Park Service began a legal battle to assert custody of the crash site and protect it from mistreatment.

The NPS claims jurisdiction over the Overton Arm wreck. The aircraft lies within the bounds of the Lake Mead National Recreation Area and is a National Historic Landmark.

In 2002, contractors for the NPS explored the wreck using a remotely-operated submarine. They found ropes and lights from previous visits, and worked out how the big plane skipped and yawed across the water before sinking to the bottom.

Its damaged windshield, bomb bay doors, landing gear, and remaining propeller all testified to the violence of the impact. But the aircraft's otherwise good condition affirmed its safe landing.

The same year — and again in 2003 — the Park Service sponsored teams of technical divers who surveyed the B-29. The plane was almost 300 feet deep, beyond the reach of recreational visits.

Divers going that low require a special helium-rich gas mixture and multiple backup systems. It takes hours of decompression to safely return to the surface. Running out of air isn't an option.

The technical divers found signs of damage and looting. In response, the NPS barred all further diving on the site until 2007.

That year, two licensed dive operators led a few hardy explorers on tours of the wreck. The NPS placed fixed moorings to prevent damage from boat anchors, and ran guide lines to the bomber. Though judged a success, the Park Service halted dive authorizations because of a limited market.

Extreme drought in much of the western United States changed those calculations. With Lake Mead's water levels at an all-time low, the Overton Arm B-29 now sits in only 110 feet of water, within reach of advanced recreational scuba divers.

If all goes well, this summer may see the first recreational dives to the Overton Arm bomber open to the general public. With effort and care, this special piece of aviation and Cold War history should amaze generations of history buffs.

Where else can you dive to the sole sunken B-29 in the world? Nowhere.

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