Stricken Soviet Nuclear Sub Sinks : Crew Evacuated; Vessel Goes Down 3 Days After Fire

Three days after it was hit by a violent explosion and fire, a Soviet nuclear submarine flooded and sank in 18,000 feet of water northeast of Bermuda early Monday, taking its nuclear-tipped missiles and nuclear power plant to the bottom.

Pentagon officials said the stricken vessel went down about 4 a.m. EDT, shortly after crewmen, illuminated by red and green flares, were seen leaving the deck and boarding lifeboats. A U.S. Navy tugboat radioed an offer of assistance but was told to stand clear.

The submarine, believed to be carrying 16 ballistic missiles armed with nuclear warheads, had managed to move about 80 miles from the site where it surfaced Friday with smoke pouring from the damaged hatch of a missile tube. The area where it sank was about 560 nautical miles northeast of Bermuda and 1,060 miles east of Cape Hatteras, N.C.

Normally Carries 120

In Moscow, the Tass news agency reported that all the crew members who survived the initial explosion and fire were safely evacuated. The size of the crew was not specified, but the sub normally carries a complement of about 120.

Tass said an investigation is continuing into the cause of the accident. The immediate cause of the sinking was “the speedy flooding of water from the outside,” the news agency said.

The day before it sank, its crew put it on a tortuous course toward Soviet waters. The submarine labored along under its own power for a time, then was towed by a Soviet merchant ship.

About four hours before it disappeared beneath the surface, the vessel dropped its tow line, and a U.S. Navy patrol reported that it was riding lower in the water, indicating that the 9,600-ton craft was gradually filling with water.

The drama at sea gained extraordinary attention in part because the Soviet Union sharply departed from its customary practice of secrecy, disclosing that the accident had claimed the lives of three crewmen, though U.S. officials believe that the toll was understated.

Twenty-four hours after the emergency began Friday, the Soviet government assured the United States that there was no danger of a nuclear explosion or of radioactive contamination of the environment. U.S. officials said that the most likely reasons for Moscow’s relative forthrightness were the scheduled meeting between President Reagan and Soviet leader Mikhail S. Gorbachev and recent criticism of the Soviets’ handling of the Chernobyl nuclear plant disaster.

On Monday, Pentagon officials said that analyses of air and water samples from the area showed no evidence of radiation above normal levels, and they discounted the possibility of any radiation hazard from the missile warheads or the twin reactors in the submarine’s power plant.

Vice Adm. Powell F. Carter said the reactor fuel plates would corrode “maybe a fraction of a millimeter per thousand years” and are in a reactor pressure vessel “which would take forever to corrode through.” Any radioactive contamination from the warheads in the distant future, he said, would be so diluted that it would be undetectable.

Because the Soviet evacuation was orderly and planned, Carter said he presumed that the reactors were shut off before the vessel was abandoned. Even if the crew did not deactivate them, he added, they would have automatically shut down after the submarine sank.

The United States has periodically taken sea water samples where two U.S. nuclear submarines went down and has seen no increase in radiation levels. The submarine Thresher sank off the coast of New England in 1963, and the Scorpion was lost off the Azores in 1968.

Compartment Flooding

Pentagon officials said they were unable to determine whether the explosion aboard the Soviet submarine ruptured the hull of the 20-year-old vessel or if the accident damaged its sea water system, causing it to flood internal compartments.

Photographs of the submarine attested to the violence of the explosion, showing heavy damage to the vault-like hatch on one of the tubes that hold the submarine’s 1,800-mile-range missiles. “That’s been torn completely loose and bent like a pretzel, so the force of the explosion was enormous when it came up through that tube,” Adm. Carter said.

Speculation on the source of the accident centered on the highly volatile and toxic liquid fuel in the missiles.

One former defense official, familiar with both submarine operations and rocket propellants, cited a continuous battle waged against corrosion and fuel spills in liquid missile systems. “It’s just a miracle that this doesn’t happen more often that it does,” he said.

If the deaths were limited to the three crewmen announced by the Soviets, sources said, it was because the compartment containing the missile tubes was sealed at the time of the explosion, as is ordinarily the case. The only crewmen in the compartment housing a submarine’s missile tubes are those passing through on their way to other compartments.

Still, the extent of the damage caused many to assume, as Defense Secretary Caspar W. Weinberger said Sunday, that the casualties were more extensive than the Soviets have indicated.