Scientists diving off the California coastline to investigate the wreck of the SS Montebello, an oil tanker sunk in 1941 by a Japanese submarine, reported Thursday that the ship — which was believed to hold up to 3 million gallons of oil — had none of it remaining.

The news came as a relief to biologists, the Coast Guard and environmental groups, who were worried that the hull of the ship, sitting in 1,000 feet of water six miles west of Cambria, might one day rust open, potentially causing a huge oil spill across the California coast.

But after more than a week of high-tech imaging and drilling into the side of the aging hulk, scientists confirmed that the sunken ship’s 32 oil tanks now hold only seawater. In other words, enough oil to fill the gas tanks of roughly 70,000 cars is gone, and nobody knows what happened to it.

“It could have been a slow gradual leak over many years since 1941. It could have all come up the day the ship was sunk in 1941. Basically, who knows? We’ll probably never know,” said Coast Guard spokesman Adam Eggers.

After Pearl Harbor

Environmental groups cheered the news.

“Stories featuring sunken boats and large volumes of oil don’t usually have a happy ending. It’s a welcome change,” said Kaitilin Gaffney, Pacific program director for the Ocean Conservancy, an environmental group with offices in Santa Cruz.

The attack on the Montebello is not widely known today. But the ship’s sinking made big headlines in 1941.

On Dec. 23, 1941, just 16 days after the bombing of Pearl Harbor, the tanker left Port San Luis in San Luis Obispo County shortly after 1 a.m., bound north for refineries in British Columbia.

Documents show the ship was carrying 75,346 barrels of crude oil — about 3.1 million gallons. By comparison, the Exxon Valdez spilled 11 million gallons into Alaska’s Prince William Sound.

Only four hours after leaving port, a lookout spotted a Japanese submarine surfacing about 100 yards away. The Montebello made a futile attempt to outrun the sub. At 5:55 a.m., a torpedo ripped into the doomed tanker’s bow.

The submarine then began shelling the tanker with a deck gun while 38 crew members raced for the lifeboats. The ship sank quickly, but all of its crew escaped to safety after two tugboats steamed through heavy seas to assist.

The 440-foot-long ship’s whereabouts were a mystery until it was discovered in 1996. After several exploratory dives, federal and state officials decided to mount a major effort to determine if the ship was still holding the oil.

The Coast Guard, which supervised the effort with the state Office of Spill Prevention and Response, funded it with no taxpayer money. The Coast Guard hired Global Diving & Salvage, a Seattle firm, to do the investigation, paying the costs from the Oil Spill Liability Trust Fund. The federal fund was created with a 5-cent-per-barrel fee imposed on the oil industry by President George H.W. Bush after the 1989 Exxon Valdez oil spill.

No risk

Since last Tuesday, roughly 50 people have been working from a command post near Morro Bay to oversee dives into the cold, black depths. The researchers took high-tech images, similar to ultrasound, of the ship’s hull. They took sediment samples and drilled into the ship’s side, looking for oil, and then capped the holes with special valves. Lab tests on the sediment, seawater and hull steel will take place in the next few months, with a final report due out next spring.

Officials at the National Oceanic and Atmospheric Administration ran computer simulations of the tides and winds, and concluded that the oil probably leaked out slowly over many years and drifted south, with much of it evaporating, sinking or washing up over time along scattered beaches.

Other sunken ships have leaked oil in recent years. In 2002, Coast Guard salvage divers pumped 85,000 gallons of fuel from the SS Jacob Luckenbach, a freighter that sank in 1953 about 17 miles west of San Francisco. That four-month cleanup, which cost $20 million, ended regular fuel leaks that had killed as many as 50,000 seabirds between Monterey and Point Reyes National Seashore over 10 years.

“This is good news,” Eggers said of the Montebello. “We wanted to know what was in there, and if it posed a risk to the coast. And we know now it doesn’t pose a risk.”

Contact Paul Rogers at 408-920-5045.