One of the scariest thoughts is to imagine
yourself inside a submarine that is sinking uncontrollably. You likely know that given
sufficient depth, the vessel will implode due to the increasing pressure exerted
by the surrounding water. That said, I was shocked when I learned more about what
actually happens when a submarine or any submersible reaches its maximum operating
depth, also known as its “crush depth”. But how it's possible to estimate the depth of
a submarine implosions based on the sound that it makes, why it’s highly unlikely to recover the
bodies of those onboard, how the crew of a sunken submarine were once rescued from the bottom of
the ocean, and why no one, and I mean no one, has actually ever experienced the implosion
of a submarine, is Not What You Think. On November 15th, 2017, the Argentinian Submarine,
ARA San Juan disappeared a few hundred miles off the coast of Argentina. About a week later, a
report was published by the Comprehensive Nuclear Test-Ban Treaty Organisation. They claimed that
they had detected a hydro-acoustic anomaly about 30 nautical miles north of the sub’s last-known
location. The anomaly had happened a few hours after the submarine’s last contact, and the
assumption was the acoustic signal had been produced by the collapse of the pressure-hull of
ARA San Juan. But the report also stated the depth at which the submarine hull had collapsed, and I
was curious; how did they figure out the implosion depth given that the collapse would have happened
way before hitting the bottom of the ocean? During an underwater implosion or explosion,
the gas bubble that is inside the structure oscillates, collapsing and expanding continuously,
before it dissipates. This is known as the “Bubble Pulse Effect”. The frequency of the pulse
can be measured acoustically, and since the volume of air inside the submarine is known, the
depth of the collapse event can be calculated. In the case of ARA San Juan, the bubble
pulse frequency was about 4.4 Hz and the implosion depth was calculated
to be at 1,275 feet underwater. The derived depth value can then be used to
determine the energy required to produce the acoustically-detected frequency at that depth.
In this case, the energy released by the collapse was equal to the explosion of 12,500 pounds of
TNT. The surrounding water pressure was 570 PSI, and the submarine hull would have
collapsed at over 1,500 miles per hour. That sounds terrifying, and yet,
no one has actually experienced it. Of course, many have tragically
lost their lives in such accidents, but none of them would have had
the time to feel or comprehend it. It could take anywhere from 100 milliseconds
to 2 seconds for the human brain to experience pain. That’s because there is a delay for the
sensation to reach the brain, and also a delay for the brain to perceive it. With dull pains,
like when you stub your toe, it could take about 1 second until you actually feel the pain. But
if you burn your fingers, your brain experiences that a lot faster, in hundreds of milliseconds.
No need to try it at home. Someone already has! It was estimated that the pressure-hull of ARA
San Juan was completely destroyed in about 40 milliseconds. That’s less than half the time for
anyone on the submarine to consciously experience anything, including pain. Even though the crew
may have been aware that a collapse was imminent, they never experienced it as it was occurring.
Their deaths would have been instantaneous.
As for the bodies of those onboard,
they cannot really be recovered. The collapse of a submarine’s pressure hull
has some similarities to a diesel engine, in which the movement of the piston compresses the
air and the diesel fuel in a short period of time. The extreme pressure causes diesel
fuel to autoignite in the engine. Similarly, the air inside a sub could have
fairly high concentrations of hydrocarbon vapors. Things like hydraulic oil, diesel
oil from the auxiliary diesel engine, grease and rubber sublime to make their
way into the submarine’s atmosphere. When the hull collapses it behaves somewhat like
a very large piston on a very large diesel engine. The air can auto-ignite. And
even if the air doesn’t ignite, the extreme compression would make it extremely
hot. The sheer force of implosion followed by the oscillations of the bubble pulse effect will
not leave any bodies behind to be recovered. That said, there have been instances of people
who’ve made it out of a sunken submarine alive. For depths up to 600 feet, special
submarine escape immersion suits can protect the crew while they use an
escape hatch or a torpedo tube to get out. The ascent from 600 feet will only take 3 to
4 minutes, but it’s an extremely traumatic experience, involving panic, oxygen
narcosis, and perforated ear drums. But things get much worse when the sub is too
deep to use an escape suit. Your only chance of survival would be a Submergence Rescue
Vehicle like the Russian Priz-class vessel; a titanium hulled vehicle that can rescue up to 16
people at a time from a depth of up to 3,200 feet. Some submarines like the Russian
Typhoon class are equipped with an escape pod, but their reliability in actual
emergencies have been questionable at best. The rescue attempt of the Russian
Kursk Nuclear submarine involved several submergence rescue vehicles,
but unfortunately, the mission failed, due to the inability of Priz to
dock onto the stranded submarine. These complications are what makes the rescue
of the crew of USS Squalus a near miracle. In May of 1939, on her 19th test dive, USS
Squalus submerged, but due to a malfunction, the main air induction valve opened
when Squalus was 60 feet underwater. This caused the flooding of the aft
torpedo room, both engine rooms, and the crew's quarters, sinking the
submarine to the bottom of the ocean. Those who were in the sealed compartments had
enough air to breathe for 48 hours at best. Cut off from outside communication,
the crew released a buoy from the deck, which had a telephone attached to it, in the hopes
that the rescue team would find it. And now, all they could do … was keep calm and wait. No rescue
attempt of sunken submarines had ever succeeded beyond 40 feet. The crew of Squalus were sitting
on the ocean floor, 243 ft below the surface. Some time later, the buoy was spotted
by their sister boat, Sculpin. The two commanders were able
to exchange a couple of words, but an ocean swell caused the line to
snap. No more communication was possible. Within 24 hours, rescue ships had arrived and
they had an experimental device to deploy. It was a rescue bell. A hard-hat diver had to first
get ready and descend, to carry a downhaul cable from a winch inside the rescue bell. Once
the cable was connected to the sub, the bell was lowered into the water and then placed
exactly above the hatch of the sunken submarine. Stranded on the bottom of the ocean, the crew of
USS Squalus were thrilled to greet the rescuers. 7 sailors climbed into the bell and
were then brought up to the surface. Three more trips had to be completed
before all 33 men were rescued. But the US Navy spent another 113 days salvaging
the submarine itself. There were bodies in the sub that still needed to be recovered. The
plan was to attach pontoons to the hull of the submarine in order to raise it off the
ocean floor and then transport it back to port. To do so, the pontoons had to be first filled
with water to create negative buoyancy and descend into the water. Once attached to the
sub, air was pumped into the pontoons, which pushed the water out, making the pontoons buoyant.
During the first attempt, the pontoons attached to the bow raised too quickly, causing the bow to
rise out of water and slip out of the cables. Eventually, USS Squalus was towed back to
port on September 13th, 1939. Twenty-five bodies were recovered from the wreckage.
The body of the 26th victim was never found. In less than a year, Squalus was repaired and
recommissioned under the name USS Sailfish, which served during WWII. The crew were forbidden
from uttering the word “Squalus” while onboard the Sailfish. After decommissioning in 1945, the
conning tower was cut away and placed in a park at the Portsmouth Naval Shipyard, where memorial
ceremonies are conducted in May of each year. In case of the Titan submersible which was lost
on June 18th, 2023 when attempting to visit the wreck of RMS Titanic, the depth at which the
implosion happened was nearly 10 times more than that of ARA San Juan, meaning the water pressure
was 10 times more at the time of the accident. We will never know what the crew of 5 onboard
Titan went through in their last moments, but it is entirely possible that their
final thoughts were joyful and exhilarating, and not tainted at all by the horror of what
was about to happen a few milliseconds later.
