One of the most terrifying notions is envisioning oneself trapped within a submarine descending uncontrollably into the ocean’s depths. It is common knowledge that at great depths, the immense pressure exerted by the surrounding water can cause the vessel to collapse inward, leading to its implosion. Nevertheless, I was astounded when I delved deeper into what precisely unfolds when a submarine or any submerged craft reaches its maximum operational depth, commonly called its “crush depth.”
However, is it feasible to gauge the magnitude of a submarine implosion solely by analyzing its acoustic signature? What factors contribute to the unlikelihood of recovering the individuals aboard? In the past, how were the crew members of a sunken submarine rescued from the ocean’s depths? Furthermore, why is it that nobody, and I emphasize nobody, has ever witnessed a submarine implosion firsthand? It is not as straightforward as one might assume.
The Argentinian Submarine, ARA San Juan, vanished several hundred miles off the coast of Argentina on November 15th, 2017. Approximately one week later, the Comprehensive Nuclear-Test-Ban Treaty Organisation released a report asserting that they had detected a hydro-acoustic anomaly around 30 nautical miles north of the submarine’s last-known position. This anomaly occurred a few hours after the sub’s final communication, suggesting that the acoustic signal resulted from the collapse of the pressure hull of ARA San Juan. However, the report also provided information on the depth at which the submarine’s hull had imploded, which raised my curiosity: How did they determine the implosion depth, considering that the collapse would have occurred well before reaching the ocean floor?
In the event of an underwater implosion or explosion, the gas bubble within the structure undergoes a continuous cycle of collapse and expansion until it eventually dissipates. This phenomenon is referred to as the “Bubble Pulse Effect.” By utilizing acoustic measurements, it is possible to determine the frequency of these pulses. With knowledge of the air volume inside the submarine, it becomes feasible to calculate the depth at which the collapse occurred.
The bubble pulse frequency for the ARA San Juan incident was approximately 4.4 Hz, leading to a calculated implosion depth of 1,275 feet beneath the water’s surface.
The calculated depth value can be employed to ascertain the energy needed to generate the frequency detected by acoustics at that specific depth. In this instance, the energy released from the collapse equaled the force of a 12,500-pound TNT explosion. The water pressure in the surrounding area reached 570 pounds per square inch (PSI), and the submarine hull would have collapsed at a staggering speed exceeding 1,500 miles per hour.
This information evokes a sense of terror, yet it is essential to note that no individual has directly experienced such an event. Unfortunately, many people have tragically lost their lives in similar accidents, but none of them would have had the opportunity to perceive or comprehend the ordeal.
The human brain can perceive pain with varying durations, ranging from 100 milliseconds to 2 seconds. This delay occurs due to the time it takes for the sensation to travel to the brain and for the brain to process it. For instance, in the case of dull pain like stubbing your toe, it may take around 1 second until you feel the pain. However, when burning your fingers, the brain registers the sensation much faster, within hundreds of milliseconds. It’s important to note that attempting such experiments at home is unnecessary since others have already done so.
In the tragic ARA San Juan incident, it was estimated that the submarine’s pressure hull was utterly destroyed in a brief span of 40 milliseconds. This duration is less than half the time required for anyone on board to experience anything, including pain consciously. Despite the crew potentially being aware of the impending collapse, they never had the chance to experience it in real time. Their deaths would have been instantaneous.
Regarding the individuals aboard, their bodies are unlikely to be recovered.
The occurrence of a submarine’s pressure hull collapsing bears resemblances to the functioning of a diesel engine, where the piston’s motion compresses air and diesel fuel within a short timeframe.
The immense pressure leads to the engine’s spontaneous ignition of diesel fuel.
Likewise, the air inside a submarine may contain significant concentrations of hydrocarbon vapors.
Substances such as hydraulic oil, auxiliary diesel engine fuel, grease, and rubber transform into vapors that permeate the submarine’s atmosphere.
When the hull collapses, it exhibits behavior similar to an enormous piston in a massive diesel engine.
The ignition of air can occur spontaneously; if it doesn’t ignite, the intense compression will generate extreme heat. The powerful implosion force, combined with the subsequent oscillations of the bubble pulse effect, would prevent any bodies from being recovered.
Nevertheless, there have been cases where individuals survived a submerged submarine incident.
For depths of up to 600 feet, specialized submarine escape immersion suits can safeguard the crew members as they use either an escape hatch or a torpedo tube to exit.
Ascending from a depth of 600 feet typically takes around 3 to 4 minutes, but the experience is highly traumatic, involving feelings of panic, oxygen narcosis, and potential damage to the eardrums.
However, the situation worsens when the submarine is too deep to employ an escape suit. In such cases, the only hope for survival would be a Submergence Rescue Vehicle like the Russian Priz-class vessel—a vehicle constructed with a titanium hull capable of rescuing up to 16 individuals simultaneously from depths up to 3,200 feet.
Submarines such as the Russian Typhoon class are equipped with an escape pod, although their reliability is highly questionable during actual emergencies.
Several submergence rescue vehicles were employed during the rescue operation of the Russian Kursk Nuclear submarine. Unfortunately, the mission failed as the Priz could not dock with the stranded submarine.
These complications highlight the remarkable nature of the crew rescue of the USS Squalus.
In May of 1939, during its 19th test dive, the USS Squalus submerged. However, a malfunction occurred, causing the primary air induction valve to open when the submarine was 60 feet underwater.
This resulted in flooding the aft torpedo room, both engine rooms, and the crew’s quarters, causing the submarine to sink to the ocean floor.
Those confined within the sealed compartments had a maximum of 48 hours’ worth of breathable air.
Isolated from the outside world, the crew launched a buoy equipped with a telephone from the deck, hoping the rescue team would discover it. From then on, their only option was to remain calm and wait. Historically, no rescue mission for sunken submarines had succeeded beyond 40 feet. In the case of the Squalus, its crew found themselves resting on the ocean floor, a daunting 243 feet below the surface.
After some time, the buoy was sighted by the Sculpin, their sister boat.
The two commanders exchanged a few words before an ocean swell caused the line to snap, rendering further communication impossible.
Within 24 hours, rescue vessels arrived at the scene, equipped with a groundbreaking contraption for deployment. This innovative device took the form of a rescue bell. To initiate the rescue operation, a skilled diver donned a hard hat and made the necessary preparations before descending into the depths. The diver aimed to secure a sturdy cable from a winch within the rescue bell. Once the line was successfully connected to the submerged vessel, the bell was gradually lowered into the water, eventually aligning precisely above the hatch of the sunken submarine. The stranded crew of the USS Squalus, isolated on the ocean floor, experienced a surge of joy upon the arrival of their rescuers.
A total of 7 sailors boarded the bell and were subsequently lifted to the surface. This process had to be repeated thrice until all 33 individuals were rescued. However, the US Navy devoted an additional 113 days to salvage the submarine. Within the submerged vessel, they remained in the solemn task of recovering the bodies still present. The salvage operation involved attaching pontoons to the submarine’s hull, enabling it to be raised from the ocean floor and transported back to port.
To accomplish this, the pontoons must be filled with water to create negative buoyancy and descend into the water. Once they were attached to the submarine, the air was pumped into the pontoons, displacing the water and making them buoyant. However, during the initial attempt, the floats attached to the bow rose too quickly, causing the bubble to lift out of the water and slip out of the cables. As a result, the USS Squalus was eventually towed back to port on September 13th, 1939. From the wreckage, twenty-five bodies were recovered, while the body of the 26th victim was never found.
In less than a year, the Squalus underwent repairs and was recommissioned with the name USS Sailfish, serving during World War II. Onboard the Sailfish, the crew members were prohibited from mentioning “Squalus.” Following its decommissioning in 1945, the conning tower was separated and placed in a park at the Portsmouth Naval Shipyard. Every year in May, memorial ceremonies are conducted at this location.
Regarding the Titan submersible, which tragically disappeared on June 18th, 2023, during its mission to explore the RMS Titanic wreckage, the implosion occurred at a depth nearly ten times greater than that of the ARA San Juan. Consequently, the water pressure during the accident was ten times more intense. While we can only speculate about the experiences of the five crew members aboard the Titan during their final moments, it is conceivable that their thoughts were filled with joy and excitement rather than overshadowed by the impending horror that would unfold milliseconds later.