Inside DOD   Know Your Military

Escape From Below: The Pressurized Sub Escape Trainer

Nov. 13, 2020

The Navy’s submarine force, known as the “silent service,” has thrived in the depths of the world’s oceans for more than 100 years. But what if a sub isn’t able to resurface? 

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At the Navy Submarine School at Naval Submarine Base New London in Groton, Connecticut, submariner students learn how to survive that worst-case scenario during a two-day class at a state-of-the-art facility at Momsen Hall.

"What we do here is we teach real-time submarine escape," said Petty Officer 3rd Class Anthony Clark, a Navy diver and instructor at the Submarine Escape Trainer. "Knowing how subs operate -- it's never in a good place, it's never in the Caribbean, and it's always someplace you don't want to be."

A man with his eyes shut is submerged in water above his nose.
sub escape trainer
Navy Petty Officer 2nd Class Frank Phelan, a diver, performs a breathing exercise to improve lung capacity. Submariner students at Navy Submarine School on Naval Submarine Base New London in Groton, Conn., are taught how to survive during a submarine escape in a two-day class at Momsen Hall.
Photo By: Navy Petty Officer 2nd Class Ignacio D. Perez
VIRIN: 160816-N-TC437-0026

On the first day of training, students go through a medical screening and are tested on their ability to perform the Valsalva maneuver -- the attempted forceful exhalation against a closed airway, which is the same way you may try to clear your ears when flying.

"We want to make sure their body can undertake pressure before we even get to the pressure testing," Clark said. "Some people's anatomies just can't do it."

Two men hold onto straps attached to a third man facing an underwater portal in a large tank. Two other men watch.
sub escape trainer
Sailors attached to the Pressurized Submarine Escape Trainer watch as a student performs a breath rate test during a pressurized escape training evolution. Submariner students at Navy Submarine School on Naval Submarine Base New London in Groton, Conn., are taught how to survive during a submarine escape in a two-day class at Momsen Hall.
Photo By: Navy Petty Officer 2nd Class Ignacio D. Perez
VIRIN: 160816-N-TC437-0207

Candidates who have successfully performed the Valsalva maneuver will then be subject to increased pressure in a dive recompression chamber with a dive medical technician. 

Though the dive chamber is at sea level, inside, the students feel like they are 60 feet below the surface. Pressure builds within the chamber until it’s equal to water pressure at "escape depth." If the student is unable to perform the Valsalva maneuver, the test stops and pressure is slowly released so he or she can exit. 

Students then learn about the physiological challenges of making a pressurized escape before moving to more rigorous training in the water.

"Our biggest concern here is POIS, or pulmonary overinflation syndrome, that involves having gas-filled spaces in your body expanding to the point where they rupture," said Petty Officer 2nd Class Frank Phelan, a Navy diver and high-risk training instructor. "We don't want that happening, so we teach the students to never ever hold their breath." 

A graphic shows four stairwells leading to the bottom of a deep pool. There is a small compartment to the left of the pool and directly below it.
sub escape trainer
A graphic shows the schematics of the Submarine Escape Trainer at Naval Submarine Base New London in Groton, Conn., where all submariners learn how to escape from a sub that is unable to resurface.
Photo By: Navy
VIRIN: 161101-D-MO260-0001A

Next up: Getting into an 84,000-gallon circular tank. It’s 20 feet wide by 37 feet deep and is heated to 90 degrees Fahrenheit. One by one, students take a deep breath, submerge into  the tank and start to blow bubbles. The goal: to make sure the rate of their exhaling breath is correct and that they get used to never holding their breath.

The students then put on life jackets and, a few decks below the surface, enter a room where a large panel displays gauges and valves. Four at a time, the students and an instructor enter a small chamber, which begins to fill with water. When it reaches neck level, the students wait for another hatch to open 15 feet below the surface. Waiting outside in that big tank are two more instructors. 

One at a time, the students take a deep breath inside the chamber and duck through the hatch. The instructors watch their breath rate to ensure they’re exhaling all the way to the surface.

A man faces away from the camera as several shirtless, blurred men stand before him.
sub escape trainer
Navy Diver 2nd Class Frank Phelan instructs students on the training exercises they will be performing during pressurized submarine escape training. Submariner students at Navy Submarine School on Naval Submarine Base New London in Groton, Conn., are taught how to survive during a submarine escape in a two-day class at Momsen Hall.
Photo By: Navy Petty Officer 2nd Class Ignacio D. Perez
VIRIN: 160816-N-TC437-0290

After passing this portion, the students head back up to the top of the tank to complete their final test: escaping from the bottom.

"If they were to hold their breath, that could lead to an array of problems -- the worst case scenario being death," said Phelan. "That's what makes this some of the most dangerous training in the Navy."

Several men stand together in what appears to be a poorly lit water tank. Some have life vests over their necks.
sub escape trainer
Sailors attached to the Pressurized Submarine Escape Trainer instruct students during a pressurized escape training evolution. Submariner students at Navy Submarine School on Naval Submarine Base New London in Groton, Conn., are taught how to survive during a submarine escape in a two-day class at Momsen Hall.
Photo By: Navy Petty Officer 2nd Class Ignacio D. Perez
VIRIN: 160816-N-TC437-0097

Students also learn surface survival. Donning bright orange suits, the students enter the tank with an instructor and a small one-man raft. The students have to prove they can successfully get into the raft unassisted, zip it closed, and drain out any water that may have gotten in it. Once done, the instructor flips the raft upside down -- as a wave might do -- and the student must get out safely while it’s still upside-down.

If at any point a student cannot complete a stage, he or she will not be rejected as unfit for submarine service -- but they won't be allowed to proceed further with pressurized training.

This blog was adapted from an article originally published in AllHands Magazine on April 29, 2019.