Wednesday, April 12, 2006

Disaster in the Deep


American Heritage
By Jack Kelly
April 10, 2006
The Thresher at sea in July 1961.
(Naval Historical Center)

“Experiencing minor difficulty.” It was 9:13 on the morning of April 10, 1963—43 years ago today—when Captain John W. Harvey relayed this message from his submarine, the USS Thresher. Harvey had steered out beyond the undersea cliff that marks the edge of the continental shelf, 220 miles east of Cape Cod. He was spiraling down to a “test depth” of some 1,000 feet. If anything went wrong that far down, the Thresher would be beyond help.

The ocean floor was now more than 8,000 feet below the boat. And things were going very wrong. The Thresher, which had been described by one admiral as “the most advanced operational attack submarine in the world,” had lost power. Unable to maneuver, its ballast tanks full of sea water to assist diving, the vessel was beginning to sink. The sea was exerting tremendous, groaning pressure on its hull. It would very soon reach a point where its steel skin would rip open. Harvey had to do something quick.

“Have positive up-angle. Attempting to blow . . .” was the rest of the message picked up by the escort vessel that floated almost a quarter mile overhead. Harvey had angled the sub’s fins to bring its nose toward the surface and was trying to empty the ballast tanks. His life and the lives of 128 other men depended on the success of the maneuver.

The Thresher represented the cutting edge of America’s military might. When Rear Admiral Hyman G. Rickover had proposed a nuclear-powered submarine immediately following World War II, skeptics had scoffed. The standard atomic reactor of the day occupied two city blocks. That it could be miniaturized to fit into a 32-foot-wide boat seemed preposterous.

But Rickover persisted; he proved the concept with the launch of the USS Nautilus in 1954. The Cold War value of the submarine, whether in its traditional attack role or as a platform for firing nuclear missiles, spurred an intensive development effort. The Thresher was a big step forward. Its teardrop-shaped hull and powerful nuclear turbine allowed speeds up to 40 knots underwater. Advanced quieting technologies let it run in virtual silence. It could detect and destroy hostile submarines from unprecedented depths.

Launched in 1960, the boat represented the first of a new class of subs. After testing the vessel at sea, the Navy ordered it to drydock in 1962 for an extensive overhaul. Assigned a new skipper, the submarine was on April 10 conducting its first trials following those repairs.

“The most dangerous condition that exists in the Thresher,” said its first captain, Rear Admiral Dean Axene, “is the danger of salt water flooding while at or near test depth.” The remark highlighted a crucial issue. The pipes that brought seawater into the ship for cooling had to withstand tremendous pressure when the vessel submerged. The joints in this system had passed tests that subjected them to even greater pressure. But a new testing method, using ultrasound, had found flaws in the workmanship of 14 percent of a sample of them. These controversial results did not prompt further repairs. Navy analysts later speculated that one of those joints gave way in the Thresher’s engine room. Spray probably shorted out electric-power components, automatically shutting the reactor.

With full power, Harvey could have muscled the boat to the surface even with its ballast tanks full. But once the reactor “scrammed,” it would take him at least seven minutes to restore power. During that time, the boat would continue to sink, quickly reaching a “crush depth” where its hull couldn’t withstand the pressure.

A roaring hiss of compressed air resonated through the sub as Harvey tried to force water out of the ballast tanks. The process was too slow. Tests later showed that it was impeded by ill-planned screening that caused ice to accumulate on a valve.

The Thresher, powerless and unable to blow ballast, began to accelerate toward the bottom. At 9:17, listeners on the escort vessel heard a garbled message that might have been “Exceeding test depth . . . ” Almost immediately, they picked up what was described as a thud or “the sound of a compartment collapsing.”

The Thresher’s hull gave way. Inrushing seawater spiked air pressure, quickly killing the crew. The pressure also ignited the sub’s diesel fuel, causing an explosion that tore the high-tech vessel to pieces.

Four months later, the bathyscaphe Trieste descended into the black depths and found an area of debris “like a large automobile junkyard.” Operators recovered a twisted piece of pipe marked with the Thresher’s name, ending the search for the ill-fated vessel. The loss of the Thresher, coming only months after the Cuban missile crisis, dealt a serious blow to U.S. power and prestige. The accident threw years of technical planning into question. Morale in the submarine service plummeted.

Governmental inquiries parceled the blame widely. In effect the sub program had leapt into a new technological realm without establishing adequate quality control. As an institution, the Navy had echoed the sentiments of former Thresher crewman Keith Johnson. “We felt invincible,” he said. “We never thought we were going to die.”

The Navy brass learned from its costly mistake. Rickover ordered a redesign of the reactor system to allow for a faster recovery from a shutdown. A new, more adequate system for blowing ballast was installed in submarines. More important, the government introduced a system, the SubSafe Program, that tightened specifications and quality assurance dramatically. Begun a few months after the Thresher’s demise, the program has yielded an exemplary safety record ever since. Sixteen American subs had sunk for non-combat reasons up to the time of the Thresher; only one has been lost since—the USS Scorpion, which sank in 1968 and had not been certified by the program.

We sometimes forget that the Cold War had costs that are both painful and difficult to reckon. The human toll of the Thresher accident was grievous. Even today, the Thresher’s nuclear reactor, with its complement of radioactive isotopes, remains at the bottom of the ocean, along with those of other sunken Soviet and American subs. With no effort currently envisioned to clean up this deadly detritus, the final bill is almost certain to be left to generations yet unborn.



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