By James Donahue

During the height of the Cold War, the U.S. Navy’s newest and most sophisticated nuclear attack submarine, USS Thresher, under the command of Comdr. Dean W. Axene, was conducting sea trials off the coast of New England when something went wrong. The 278-foot-long submarine sank in 8,400 feet of water, taking 16 officers, 96 enlisted men and 17 civilian technicians to a quick but terrible death.

The Thresher had just been given an overhaul following a collision with a berthing tug at Port Canaveral, Florida, and was on deep-dive trials, with the Navy submarine rescue ship Skylark steaming overhead, when the accident happened shortly after 9 a.m. on April 10, 1963.

Officers on the Skylark said Thresher first radioed that it was having “minor problems,” without explaining what they were. After that came several fragmentary, garbled messages. Finally at 9:18 a.m. they heard a sound “like air rushing into an air tank,” followed by the sounds on the sonar of a submarine imploding and breaking apart.

The bathyscaph Trieste was sent to the bottom and obtained photographs that showed the submarine had broken up. It was never raised, and the cause of the disaster was never known. President John F. Kennedy ordered all U.S. flags flown at half mast on all government buildings and ships from April 12 to 15. The nation was so stunned flags everywhere went to half mast in recognition of the tragedy.

A Navy board of inquiry concluded that the probable cause of the sinking was a failure in either a pipe, valve or hull weld that flooded the engine room. A fast flood like that could have shorted a main electrical bus board and caused the reactor to shut down. The emergency shut-down of the reactor resulted in a loss of steam power to the primary propulsion system, which prevented Thresher from rising to the surface. Thus the ship had negative buoyancy and sank, probably stern first.

The theory was that the crew started the submarine’s emergency propulsion system, but it was not powerful enough to push the heavy ship upward from that depth. The submarine may even have started to surface but the lines to the air pressure-reducing manifold valves iced over and froze shut, and that was the final straw. The Thresher was doomed. The continued flooding caused the ship to drop below her crush depth where the pressure of the ocean destroyed it.

The submarine was broken into six major parts strewn over the ocean floor, with most of it in a single debris field about 400 yards square. The reactor also is in that debris. Continued monitoring of the site shows no indication of a release of radioactivity from the reactor.

Commissioned in August, 1961, Thresher had been in service less than two years before it was lost. There were two major events affecting the ship during those months.

During her original sea trials, Thresher was docked at San Juan, Puerto Rico, with her reactor shut down and a diesel generator providing the electricity needed to carry out usual docking procedures. The diesel generator, however, unexpectedly failed and the crew relied on an electric storage battery for lighting to permit them to work on the generator. The problem was more severe than expected and the crew attempted to restart the reactor. But this takes several hours and the battery failed. With no ventilation system working, the submarine heated and sailors were forced to evacuate the ship after the heat rose to about 140 degrees.

The problem was solved by attaching electric lines to the diesel-electric powered submarine Cavalla which was moored alongside. With power from the Cavalla, the Thresher’s reactor was restarted.

The collision with the tug happened on June 3, 1962, at Port Canaveral, Florida. The crash left a three-foot gash in the submarine’s ballast tanks just under the water line. The Thresher went to New London, Conn., under her own power, for repairs.