Two weeks after the attack on Pearl Harbor, a Japanese submarine launched a torpedo at an American oil tanker just off the California coast, sinking the ship and possibly 3 million gallons of crude to the bottom of the ocean.

All 38 people on board were rescued and the story was largely forgotten but the legacy of this little known chapter during World War II could have significant environmental implications.

For seven decades the SS Montebello has sat mostly intact 900 feet below the surface with what experts believe could be a hull full of oil. A mission to see how much of the oil remains in the hold of the 440-foot ship launches this week to help officials determine how to prevent the crude from leaking and marring the celebrated central California coastline.

"Eventually, something has to be done," said Andrew Hughan, a spokesman with California Fish and Game. "If 3 million gallons of oil made its way to the beaches in front of Hearst Castle it would be a disaster for the area."

Divers along with a remotely-operated underwater vehicle will begin their assessment Wednesday and take samples, a process that is expected to take as many as 12 days. The vehicle will drill and later seal a 1-inch diameter hole into some of the tanks to take samples that will be analyzed by scientists.

While it's possible the oil leaked out over the past decades, officials say it's likely crude remains in the hull. By this point, the oil is so old that it likely has the consistency of peanut butter, said U.S. Coast Guard spokesman Adam Eggers.

"No one knows what 70-year-old oil does," he said. "It's 40 degrees down there. Is it going to rise to the surface, warm up and liquefy or it is going to be a rock?"

The Montebello set out from Port San Luis, Calif., on Dec. 22, 1941, bound for a refinery in Canada with fresh crude.

Crew member Richard Quincy said it was the second such trip they had taken and had been warned that Japanese submarines were in the area. The torpedo hit the ship's bow, which cracked off when the Montebello hit the ocean floor.

Quincy recalled a small spark of light as though someone had turned on a flashlight, an explosion that threw water up over the bridge, and then the ship began to sink from the torpedo hit. Quincy, a 92-year-old former merchant mariner now living in Danville, is the last remaining survivor from the sinking of the Montebello six miles off the coast of Cambria.

"We thought it might catch fire because we were carrying a volatile product," Quincy said. "Undoubtedly, it's in there somewhere because there haven't been any real hull leaks in the area."

The Montebello, meanwhile, has been sitting upright ever since. Murky pictures from previous dives show a ship partially covered in a thick coat of barnacles, starfish and marine debris.

Few knew about the Montebello's fate even immediately after it sank. Fearing a mass panic that the Japanese had gotten so close to shore, the government confiscated newspaper reports about the sinking at the time and did not publicly disclose the event even into the Cold War, said Eggers.

In fact, Japanese submarines operated along the U.S. West Coast, although they did not sink the large numbers of ships that German U-boats claimed along the East Coast and Gulf of Mexico. In addition to the Montebello, two other tankers were sunk on the coast off Oregon and Crescent City, Calif.

Among other famous World War II attacks in the American theater, submarines shelled a California oil field and an Oregon military installation, and a float plane dropped incendiary bombs in the woods near Brookings, Ore. Japan also launched thousands of bomb-laden balloons across the Pacific in a largely failed attempt to set American forests ablaze. One bomb did kill an Oregon woman and five children.

Decades after it went down, the Montebello became a concern when local efforts to memorialize the sinking led to a 1996 scientific survey that located the wreck and discovered it was mostly intact — particularly the cargo holds. The presumption that oil was still inside led to worries that a rupture could threaten the nearby Monterey Bay National Marine Sanctuary but the depth made recovery unlikely and only monitoring continued.

It wasn't until 2009 that state Sen. Sam Blakeslee, R-San Luis Obispo, learned about the potential environmental disaster from a local newspaper report about the Montebello, news that eventually prompted him to help assemble a team of federal and state officials and scientists to investigate the situation. The effort will cost $2.3 million, money that will come out of a fund that oil companies pay into for such measures.

"It was one of those issues that was really not on anyone's radar and no one really knew the ship was out there," he said. "I think that terrible incident in the Gulf of Mexico galvanized all the stakeholders to take action and be proactive and get answers given the terrible cost and environmental damaged that occurred."

A report recommending a possible course of action is expected to be released later this year.

Officials worry a potential spill from the Montebello could eclipse the massive Santa Barbara oil platform blowout that coated miles of coastline in 1969, washing ashore the bodies of dolphins and seals.

Another ship that sank in 1953 near San Francisco called the SS Jacob Luckenbach slowly leaked some of the 475,000 gallons of oil the freighter was carrying, fouling the coast for decades. The Coast Guard spent $20 million to remove oil from the ship and seal it from future leaks, which had already killed tens of thousands of sea birds.

For his part, Quincy said he intends on keeping an eye on what the mission uncovers. He's seen past videos that panned over the ship and even spotted the area where he had been standing when they were hit.

"It'll be interesting to see just how much the damage there was and where it was and all that," he said. "It would bring back a lot of memories. It was a wild night."