ARIBBONED BOTTLE of champagne burst bubbling over the hull of the nation's newest nuclear-powered attack submarine. The christening of the USS Thresher took place at the Portsmouth (N.H.) Naval Shipyard July 9, 1960, heralding a new era in U.S. Naval defense.

The submarine was the second Thresher to be commissioned. The first was a non-nuclear ship built in 1939. The new version featured the most modern technology available including nuclear reactors. Thresher was the flagship of its class and the nuclear reactor prototype. Built for strength, speed and stealth, the submarine was a pioneer of what was to become an attack nuclear submarine fleet.Less than three years after launching, however, the Thresher mysteriously sank to the ocean depths. Not only was the $5 million state-of-the-art ship lost, but so were the lives of 129 crewmen.

Like other pioneering quests gone awry, the disaster ultimately resulted in technological developments that might otherwise have been delayed or overlooked. The tragedy raised questions about the safety and design of the craft and led to improved ship construction. In fact, development of nuclear-powered submarines was actually accelerated in the shadow of the Thresher loss. Also, technological advances in deep-water oceanography and research were direct results of the search and recovery operations.

Why the Thresher sank is a mystery. The submarine's equipment gave it unusual flexibility, maneuverability, speed and stealth.

It was named after the thresher shark, which is characterized by a tail that, when extended, is longer than the combined length of its head and body.

The submarine's hull was an Albacore-type design and was capable of extremely high-speed and deep-depth operations. Thresher's technology included a remote-control torpedo firing and handling system with torpedo tubes amidship instead of at bow and stern. Thresher was capable of diving deeper and running more quietly at high speed than any U.S. submarine previously built. It cruised 2,900 miles during four sets of sea trials prior to its May 1961 commission and ran several trials and tests from August 1961 to its final departure in April 1963. In the seven months of operations following its initial sea trials, Thresher had spent more than 2,100 hours under way and steamed nearly 18,400 miles without a hint of the inherent problems that would drag it to the bottom of the sea.

Thresher had been at the Portsmouth Naval Shipyard since July 1962 for outfitting and pre-testing for the spring run. The day before its final voyage it left for routine deep-diving trials and returned from the tests without any problems. The next day, however, it was scheduled to push beyond deep-depth frontiers.

On the morning of April 10, 1963, escorted by the submarine rescue ship Skylark, Thresher slipped out of the bay of Boston to engage in extensive deep diving and research. The long-tailed metal shark sped 220 miles east of Boston. The skipper, Lt. Cmdr. John Harvey, was not new to nuclear subs or frontiers. He had served in the initial nuclear submarine cruise under the North Pole in the Nautilus.

The Skylark bobbed on top of the water while the Thresher began its dive to a classified depth. Within 15 minutes from reaching the test depth the Thresher signaled it was in trouble. The Skylark received the brief message at 9:13 a.m.: "Experiencing minor difficulty. Have position `up' angle. Attempting to blow. Will keep you informed."

That meant Thresher was trying to surface. The next thing heard was the sound of rushing air and water as of a ship breaking up undersea. The Skylark's urgent request for additional help was answered by the submarine rescue ship Recovery, which arrived to find only a lingering oil slick. Behind the telltale slick floated other debris including cork and plastic identified as material used in the internal construction of submarines of Thresher's type. Other items found in the area were two yellow gloves, two bottles containing liquid and a tube of "Baker's Flavoring." No bodies were recovered. Sixteen officers, 96 crewmen and seventeen civilian technicians were swallowed up in the disaster 25 years ago. Both the Skylark and Recovery lacked the technical equipment to search the depths to which the Thresher had plunged.

One crew member, Raymond A. McCoole, was saved from the swift sinking by another quirk of fate. McCoole was already aboard the Thresher that spring morning preparing to launch as planned. His wife, Barbara, was at home caring for their daughter, and as she attempted to open a bottle of liniment, the glass container exploded in her face.

Barbara was rushed to the shipyard infirmary at Portsmouth, and Thresher's executive officer, Pat M. Garner, was told about the accident. Since the extent of injury was not immediately known and the small child would need someone to care for her, Garner and Skipper Harvey decided to send McCoole ashore to be with his wife.

McCoole left the Thresher with some disappointment at not being able to complete the deep-depth testing. He had sailed with Skipper Harvey on the Nautilus under the Arctic icecap and had looked forward to this rendezvous. Reflecting on the disaster, McCoole now wonders whether circumstances would have been different if he had stayed on board. He was the safety officer of the ship, and perhaps he could have prevented the tragedy. Or, he might have been No. 130 lost at sea.

Search and rescue operations followed for the next five months of 1963 with more than three dozen ships and thousands of men detailing the ocean floor. The exhaustive search found the Thresher in 8,400 feet of water. The area became the most searched part of the ocean at that depth in the world. The bathyscaph Trieste took ten dives to explore what would be called the Thresher Area.

Additional exploration took place in 1964 by Trieste II, which found the wreckage and took pictures of the tail section, stern planes and topside rudder. The submarine's sail and the attached sail plane were also photographed.

A court of inquiry concluded the reason for the disaster was the failure of some safety system that was impaired at the depth research was to take place. The case resulted in many changes in submarines and the emergence of a submarine safety center. The inquiry ended in June 1963 after producing 1,718 pages of testimony, reporting 166 pertinent facts, offering 54 opinions and making 20 recommendations.

Changes that resulted from the Thresher disaster included:

*Immediate restrictions on operating depth;

*Construction modifications to provide a low-pressure system for auxiliary sea-water service;

*Provision of the remote hydraulic operation of all sea and hull valves and placement of operation stations at different locations so that a leak at one would not prevent access to the other stations;

*Replacement of sil-braze joints with welded joints throughout the piping systems; and

*Modification of the air systems, which significantly increased the submarine's capability to recover from a flooding casualty.

Since the Thresher tragedy, only one other nuclear submarine, the USS Scorpion, has been lost. That submarine disappeared in May 1965 in the Bermuda Triangle off the Azores taking 99 officers and men with it. No known cause of the Scorpion's disappearance has been found.