Two hundred and twenty miles East off the coast of Cape Cod lays the remains of one of the worst submarine disasters in the history of the U.S. Submarine Force. This week we remembered the USS Thresher and those who were lost 55 years ago. We also ask, how did this happen?

There were nine classes of submarines created before the Thresher. With each class, the Navy believed that they could do better. Before mass producing a specific kind of submarine, they knew that the design had to be perfect. The Thresher class of submarines was the first to have more than five ships built. They were built to be fast and deep-diving. They were the second class behind the Skipjack to be designed with a new streamlined hull that is still in use today. The Threshers were the first to use HY-80 steel alloy that would be used through the 1980’s. Built 30 percent larger than the Skipjack class, they weighed 4,369 tons while submerged. The primary sensor was the first bow-mounted sonar installed in an attack submarine. This moved the four torpedo tubes back, which is a design still used in the Virginia class. Carrying Mark 37 homing torpedos, Mark 57 deep water mines, Mark 60 CAPTOR mines and the SUBROC antisubmarine weapon, the Thresher would be the most powerful submarine to join the fleet. But in April of 1963, that power would be brought to the bottom of the ocean under 8,400 feet of water, and 129 lives ended before their time.

On April 9, 1963, the USS Thresher was conducting test dives off the coast of Cape Cod. Even though she had been in service for two years, The Navy was conducting more tests to determine how much strength the hull could truly withstand. The submarine rescue ship USS Skylark was waiting on the surface should anything happen. At nine in the morning, Thresher reported to Skylark that they were experiencing minor difficulties. Two more inaudible messages were sent before there was eerie silence. The Thresher was never heard from again. She was at a test depth of 1,300 feet. The hull was found ruptured into six pieces.  The question on everyone’s mind after the loss was how this could have happened. To this day, the submarine force prides itself on safety. Every effort is made on keeping the crew of the submarines as safe as they can be. Rickover, the father of the nuclear Navy, was known for being overbearing and at times extremely difficult in order to maintain safety regulations onboard ships. However, in the 1960’s, there was still a lot to learn about submarines – from developmental practices to the best materials to use. The best theory to have come from years of investigations has been that the use of silver brazing on the piping throughout the ship was to blame. It is estimated that three thousand silver-brazed joints were used on Thresher. The process of silver brazing involves a non-ferrous filler metal that is heated to melting temperature and distributed between two or more parts. It is believed that some of these joints were improperly made, causing a pipe to experience joint failure. As seawater came through the pipe, it shorted one of the main electrical boards and caused a loss of power aboard the vessel.

In 2003, a Navy testimony showed that the crew of the Thresher was unable to access equipment that was needed to stop the flooding from the failed pipe. As she took on water, the submarine’s ballast tanks failed to operate. Investigations show that restrictions on and moisture in the air system led to a buildup of ice on the valves which prevented them from being able to operate properly. The Navy was extremely quick after the loss to make sure that the lives of the 129 on board would not be in vain. Less than two months later, SUBSAFE was created to prevent another tragedy like the Thresher. The Submarine Safety Program is a quality assurance program that covers all systems exposed to sea pressure or that are critical to flooding recovery. Between 1915 and 1963, 16 submarines were lost due to non-combat related causes. Since the creation of SUBSAFE, only one submarine has been lost. SUBSAFE certification has four key areas- Design, Material, Fabrication and Testing. During each step, testing is done in order to make sure each element is up to standard. All work done, and materials used that relate to sea pressure are controlled by specific guidelines set forth in the certification manual. Every part is tracked and tested from its point of creation to its insulation. While these measures have created an extra cost with submarine development, it is a cost that has saved countless lives since 1963 and one everyone is willing to pay. While SUBSAFE only addresses the quality control for flooding concerns, other programs are in place to regulate safety concerns such as fire safety, weapons systems, and nuclear reactor safety.

The loss of the USS Thresher will forever be a part of the submarine force’s collective memory. The creation of SUBSAFE and every precaution that has bee taken since is in honor of those men we lost on April 10, 1963. The men and women who choose the submarine force are choosing a service that is still highly unknown. A submarine sails silently underneath the waves, leaving no trace of where it has been or where it is going. Extreme pressure from the water that surrounds the steel hull is consistently beating against it. We must protect those that dive to great depths to protect us here and abroad. The loss of the Thresher is a reminder that we must always do better. Rigid guidelines and advanced testing has led to countless lives saved. But to continue doing better we must remember and honor those that came before and will never be forgotten.