After more than 60 years — and some of the most intense action that a military vessel has ever seen — a World War II-era aircraft carrier has recently been re-discovered off the coast of San Francisco, still larded with its final cargo: hundreds of barrels of radioactive waste.

The U.S.S. Independence was found in April by archaeologists using sonar-equipped submersible vehicles near the Farallon Islands, some 65 kilometers from San Francisco, California, not far from where it was intentionally sunk by the U.S. Navy 64 years ago.

The vessel is said to be “amazingly intact,” with its hull and deck still visible, including what appears to be at least one airplane still in its hangar bay.

“After 64 years on the seafloor, Independence sits on the bottom as if ready to launch its planes,” said James Delgado, maritime heritage director for the Office of National Marine Sanctuaries, in a press statement.

Moreover, this week, nuclear scientists from the Lawrence Berkeley National Laboratory determined that the ship’s toxic cargo, while presumably still intact, is not detectable far outside the confines of the ship.

At the request of Delgado’s team, the Berkeley Lab conducted tests on the submersibles used to study the shipwreck and found no traces of radioactive contamination.

“They wanted to know if we could ensure the safety of their equipment and to see if you’d pick up contamination if you went down there,” said the Berkeley Lab’s Dr. Kai Vetter, in a statement.

“The short answer,” according to the lab’s press office, “is that neither the submersible nor the team was ever in danger of contamination.”

The story of how an aircraft carrier freighted with nuclear waste came to sit off the shores of a major American city begins in 1943, when the U.S.S. Independence was converted from a cruiser and commissioned to fight in the Pacific during World War II.

It saw combat duty from November 1943 to August 1945 at the Gilbert Islands, the Philippines, and Okinawa, after which it was assigned a new mission: to be a target for nuclear bombs in the Marshall Island’s Bikini Atoll.

There, in the summer of 1946, it was a test-piece in Operation Crossroads, a pair of low-elevation detonations designed to study the effects of nuclear weapons on warships.

The Independence survived the highly publicized blasts, but was badly damaged and irradiated, and was brought back to San Francisco in August 1946. [See another WWII vessel recently discovered in Hawaii: “Sunken WWII Ship, Famed for Pearl Harbor Rescue Mission, Discovered Off Hawaii Coast“]

“This ship fought a long, hard war in the Pacific and after the war was subjected to two atomic blasts that ripped through the ship,” Delgado said.

“It is a reminder of the industrial might and skill of the ‘greatest generation’ that sent not only this ship, but their loved ones to war.”

Before it was finally decommissioned in 1951, the Independence was loaded with several hundred 55-gallon barrels of radioactive waste leftover from the production of nuclear weapons, which were covered in concrete and sealed in the ship’s engine and boiler rooms.

The Independence was then sunk to a depth of 800 meters, or 2,600 feet, where it was re-discovered by Delgado’s team as part of a two-year program to find and map the 300-plus shipwrecks that now rest within the Gulf of the Farallones National Marine Sanctuary. [Read about other discoveries made by the program: “Shipwrecks Discovered in Nautical ‘Graveyard’ at San Francisco’s Golden Gate“]

As for its levels of radiation, the Berkeley Lab points out that the submersible used to find the wreck never got within 30 meters, or about 100 feet, of the ship, so “it wasn’t a surprise” that it wasn’t contaminated.

It adds that the energy from ionizing radiation, like that produced by nuclear waste, is readily absorbed by water, and that any irradiated particles, like of rust, would be “diluted” by the ocean.

The lab also acknowledged that “a relatively small number of organisms close to the wreck might take up” some of those particles, but noted that most of the materials buried there are radioactive isotopes known as cesium-137 and strontium-90, which have a half-lives of 29 to 30 years.

This means that in 30 years, half of the radioactive isotopes have decayed into more stable, and less dangerous forms, and that — after 64 years — less than a quarter of the original materials remain intact.

There are no plans to survey the ship or its contents more closely, Delgado’s office added, and the Berkeley physicists noted that studying its radioactive cargo would likely require a new technology.

“It would be exciting to build a dedicated system with some advanced technologies to figure out what is sitting down there in that old vessel,” Vetter said.