On the morning of 10 April, the ships met to conduct a depth test. At approximately 0747, the Thresher commenced a deep dive. At approximately 0913 she reported, “Experiencing minor difficulties have positive up angle. Am attempting to blow. Will keep you informed.” At approximately 0916, the Skylark heard a garbled transmission believed to include the words “ . . . test depth” and at 0917, another garbled transmission containing the words “ . . . nine hundred North” was reported. At 0918, a high-energy, low-frequency noise disturbance was observed. The water depth in the area of operations is about 8,500 feet. The Thresher , along with 129 souls, was lost that day.
After the incident, a court of inquiry and the Joint Congressional Committee on Atomic Energy hearings concluded that a flooding casualty in the engine room, resulting from a piping failure in one of the sea-water systems, was the most probable cause. On 3 June 1963, the SUBSAFE program was established within the Bureau of Ships to develop the Submarine Safety Certification Criterion, outlining the minimum actions required to provide a satisfactory level of confidence in the integrity of submarine systems and the adequacy of certain depth-control capabilities. The first effort to apply additional rigor in design, manufacturing, operation, and maintenance to a subset of critical systems within the nuclear submarine, the program’s goal was to provide maximum reasonable assurance of hull integrity to preclude flooding, and the operability and integrity of critical systems and components to control and recover from a flooding casualty, should one occur. The Bureau of Ships issued a certification criterion addressing design, material, fabrication, testing, and record keeping on 20 December 1963.
Over the next ten years, changes and improvements to the original criteria were established, and the “Submarine Material Certification Requirements Manual for the Submarine Safety Program” was issued in 1974. During this time, the Bureau of Ships evolved into the Naval Ship Systems Command and ultimately the Naval Sea Systems Command. The latter continues to review and update the administrative and technical requirements of the SUBSAFE program.
The second foundation of submarine safety, the DSS-SOC program, had its watershed event in 1982. Five divers lost their lives when a vacuum was inadvertently drawn in a lock-out chamber on the USS Grayback (SS-574), leading to increased requirements for deep-submergence systems’ design, construction, maintenance, and operation. DSS-SOC efforts are designed to provide maximum reasonable assurance that a material or procedural failure will not imperil personnel by focusing on the operability and integrity of critical systems, components, maintenance, and operational procedures. In assessing the risks to operator and occupant safety, DSS-SOC considers hazards such as breathing gases, material off-gas toxicity, flammability, implodability, explodability, electrical hazards, and procedures.
The third foundation of submarine safety, the Fly-By-Wire Ship Control Systems program, was designed and executed to provide maximum reasonable assurance that the fly-by-wire ship control system in a submarine will not cause a casualty or prevent ship recovery from flooding or a control-surface jam casualty. Instituted with the initial introduction of limited electronic fly-by-wire systems for ship control on Seawolf -class submarines, the program expanded with a much greater capability on the Virginia -class. Fortunately, this system was not the result of a tragic event. Navy engineers recognized the risk similarities between submarine fly-by-wire control systems and commercial and military aviation systems and implemented the program proactively.
While the Thresher ’s loss is the pinnacle event that led to the SUBSAFE program, much older disasters also lend perspective to our work. Submarine casualties are a rarity in modern times, but this was not always the case. From 1915 to early 1963, the Navy lost 16 submarines in non-combat related incidents—an average of one submarine lost every three years. All together, these accidents took the lives of 454 submariners.
Lessons from the H. L. Hunley
Reasons to develop all three submarine safety programs can be traced back more than 150 years ago to the sinking of the H. L. Hunley . Incredibly, she sank three times over the course of her career. All of the events that led to her sinkings share elements with the dangers facing submariners to this day and serve as a reminder of why the U.S. Navy implemented the aforementioned safety initiatives.
Originally known as “the Fish Boat,” or simply “the Boat,” the Hunley first sank on 29 August 1863 during surface operations. Lieutenant John A. Payne, the officer in charge, inadvertently stepped on the lever that actuated the dive planes, which resulted in an uncontrolled dive. With both her hatches open, she experienced uncontrolled flooding, and five of the eight men on board perished. Perhaps the first control-system casualty in the history of submarine operations, this “jam dive” produced the result that today’s Fly-By-Wire Ship Control System program is designed to prevent.
Despite the loss of life and sinking, the general in charge of Charleston’s defenses, Pierre Gustave Toutant Beauregard, saw the boat’s potential and had her salvaged and repaired. The lost men were buried, a new crew was formed, repairs were made, and she was put back to sea in less than two months. This time, she was commanded by Horace L. Hunley, her creator and financier. He helped build the submersible and therefore knew her better than anyone else. In theory, this would be safer than training people who lacked comprehensive knowledge.
On 15 October 1863, Hunley and his crew were doing training dives with a surface ship as an escort. The submersible made several dives and surfaces throughout the day and then failed to surface. Once again, Beauregard requested salvage and recovery. The divers found the boat in 54 feet of water, partially flooded, with her bow buried in the mud at a 30-degree angle. The assessment at the time was that she had suffered a ballasting problem; unable to carry the additional weight, she plowed toward the bottom at high speed. With the bow firmly stuck in the sea bed, the crew could not free the submersible, and all eight of them either drowned or were asphyxiated. This loss foreshadowed the danger of flooding and the importance of ship-recovery systems, other factors the SUBSAFE program is designed to mitigate.
Despite a track record of two sinkings and the loss of 13 men, including her inventor, the boat was raised once again, refurbished, and put back into service. And again, an eight-man crew assembled, this time with Lieutenant George Dixon in command. After further training, the Hunley prepared for her fateful mission. On the night of 17 February 1864, she departed South Carolina’s Charleston Harbor and approached the sloop-of-war USS Housatonic , a Union warship that was lying at anchor off the shore. As the Hunley approached the starboard side of the Housatonic , watchstanders spotted her and opened fire with muskets and shotguns. Then the Hunley affixed an explosive charge to the Housatonic ’s hull, using a 25-foot spar on the submersible’s bow, and detonated the charge, dooming both vessels. The Union lost five sailors from the Housatonic ’s crew, and the Confederates lost the Hunley and her entire crew when she sank soon after the attack.
The Union fleet outside of Charleston Harbor immediately knew its warship’s fate, but no one knew what happened to her attacker until 1995 when the Hunley ’s final resting place was discovered. In August 2000, she was raised once more and has been undergoing conservation and examination at the Warren Lasch Conservation Center in Charleston, South Carolina. Now that the Hunley has been salvaged and continues to be carefully preserved and examined, the mystery as to why she sank for a third and final time can hopefully be solved. What has been determined so far is that the crew was found at their stations, not crowded around the hatches trying to escape. This suggests that something other than flooding or a loss of ship control may have occurred during the attack to imperil the crew. Additionally, she was found to the seaward of the Housatonic , the opposite direction of the planned return to Confederate-controlled waters.
Taken together, a plausible explanation might be that the crew was incapacitated and the vessel was set adrift in the ebb current, eventually sinking outside the harbor. The crew’s debilitation may have been caused by the poor air circulation, which would have heightened the deprivation of oxygen. This and other similar hazards are principal risks countered by the DSS-SOC program, which exists to prevent the imperiling of the operators of a submergence vessel. While this linkage is admittedly less certain than those of the Hunley ’s first and second sinkings, it is compelling to take her entire history and align it with the programs we rely on now to protect our submarines and their crews.
The U.S. Submarine Force’s outstanding safety record since the Thresher tragedy is a direct result of rigorous compliance with the technical and administrative requirements of the SUBSAFE program. This success has not gone unnoticed. The January 2011 Report to the President of the United States, “Deepwater Horizon Gulf Oil Disaster and the Future of Offshore Drilling,” cites the SUBSAFE program as a model of an organization that successfully operates a high-risk program, referring to its “rigorous nature.” Since the program’s inception in June 1963, the United States has not lost a SUBSAFE-certified submarine.
Today’s challenge, 51 years after the Thresher ’s loss and 150 years after the Hunley ’s, is to maintain the standards established by the safety programs. Part of that effort is looking at the past to identify failures so as not to repeat them. Such retrospection is ingrained within the Submarine Force’s culture and must be continually reinforced at all levels of the submarine community. This rigorous compliance with requirements and attention to detail begins with design and extends through every aspect of construction, maintenance, and operation. The ability of submarines to continue to operate successfully depends on the vigilance and integrity of everyone who works in the submarine community.
The pressures of shrinking budgets and personnel, coupled with a workforce that has not, thankfully, endured the loss of a ship, cannot cause diversion from the principles that have taken decades to build and refine. The Submarine Force must remain vigilant in its work to avoid the three threats to the SUBSAFE program: ignorance, arrogance, and complacency. The supreme sacrifice of those lost with the Thresher and other submarines can best be remembered by never letting it happen again.