An Implosion of Monstrous Proportions

Unfortunately, submarines have been in the news a lot lately with the loss of the Titan, the submersible that imploded with five people on board while trying to view wreckage of the Titanic. While it's unlikely the Titan is going to become a footnote anytime soon there is another submersible implosion that many have forgotten about (or are unfamiliar with) as it has become just a footnote in history...

The USS Thresher

The U.S.S. Thresher

The USS Thresher was a nuclear-submarine of the United States Navy. It was commissioned in August 1940 and, as an attack class vessel, became the most decorated submarine of WWII with 15 battle stars. The Thresher was the first in a new class of attack submarines and was the culmination of over a decade of new scientific and engineering research. It was designed to dive deeper and be quieter than its counterparts. It had rubber washers installed between the metal parts to make it quieter without the noise from metal on metal contact. Additionally, changing the shape of the submarine to a tear-shaped hull allowed it to submerge better. While most WWII-era subs operated at the 400 foot mark the Threshers could dive over three times deeper at the 1,300 foot mark.

A Return to the Sea

After her career in WWII the Thresher went through a series of tests before eventually going to the Portsmouth Naval Shipyard for an extensive overhaul in 1962. She didn't return to the sea for another 18 months. In April 1963 she was scheduled for a dive to test her normal depth and set sail from Portsmouth with 129 crew members aboard, including seventeen civilian observers.

The first round of tests were shallow dives to check the hull's integrity. They dove only about 600 feet to test for leaks and she passed with no issues. The boat accompanying her, should there be need for a rescue, was the USS Skylark. After the successful tests the boat was released and told to meet back up with the Thresher 200 miles east of Cape Cod. This was past the edge of the continental shelf where the ocean's depths reached beyond 8,000 feet. The two vessels successfully met up the next morning on April 10 and more tests began.

The next test was to take the Thresher to its 1,300 foot mark. As it hit depth markers in 15 minute intervals the Thresher communicated back to the Skylark via the UQC (an underwater telephone). After reaching the 1,300 foot mark the rescue ship received a message from the Thresher that it was "experiencing minor difficulty." The submarine attempted one last communication after that message but it was unintelligible.

A Tragedy in the Sea

What happened next after the Thresher sent out its received message to the Skylark is not entirely known but several things had clearly gone wrong. The Skylark continued to attempt to message over the UQC, and even dropped signal grenades in an attempt to communicate with the submarine. Eventually the ship had to acknowledge something horribly wrong had happened and they reported the situation to the naval command, with the message going as high as President John F. Kennedy. A search and rescue began.

Some of the submarine's wreckage

It wasn't until April 22, almost two weeks after it first went missing, that any sign of the Thresher was found. The oceanographic vessel, the Atlantis II, found the submarine's anchor on the ocean floor 8,400 feet below the surface. Several dives occurred in the coming months but it wasn't until August 28 that the Trieste located a large debris field. The Trieste was a bathyscaphe, which is not a submarine but a diving vessel that can go to the very deepest of depths, including the Mariana Trench, the deepest trench in the world at over 36,000 feet down. Only bits and pieces were found among the debris. Among them was a warped copper pipe, which later served as a 'smoking gun' for what may have gone wrong.

The search for the submarine continued for another year into 1964, even though the Department of Defense released a statement a year earlier that the debris had all been discovered and recovered. The Trieste II took a more comprehensive survey of the wreck site in 1964 over an area of 33 acres.

What happened to the Thresher?

An illustration showing the depth where the Thresher sunk

Although the exact cause of the Thresher's sinking will never be known an inquiry was opened once the submarine went missing and was closed that June. By the time it closed the Navy had not even located the wreck.

Two theories arose as to what happened: a leak from an intake pipe that brought seawater in to cool the reactor or a blockage in the compressed air valve to the main ballast tank. Either way they determined the Thresher must have lost power, which prevented it from being able to move or ascend. It also prevented the crew from being able to manage the water intake through the pumps.

Regardless of what caused it, the wreckage shows what likely happened in the Thresher's final moments. Water pressure increases 44.5 pounds per square inch for every 100 feet of depth. By the time the Thresher fell to 1,900 feet it would have reached its "crush depth," leading to an implosion. When the final collapse occurred it would have taken only 100 milliseconds, with a force equivalent to 22.5 kilotons of TNT, for the submarine to implode. Whatever remained of the vessel fell to the debris field 8,400 feet below and spread over 33 acres that was eventually found by theTrieste. The implosion killed all 129 crew members onboard and became the deadliest submarine implosion to date.