When a submarine departs port, its men face the small, but very real chance that it will sink before they can return. These powerful undersea vessels are as complex as a space station. They are filled with pipes, valves, machinery, and explosives. The diligent crews that tend them follow proven operating procedures; yet there is much that can go wrong. Service aboard a submarine is, and always has been, considered hazardous duty.
If a submarine should be disabled and sink to the bottom in water less than 400 feet deep, the men trapped aboard can wait to be rescued, or they can organize an escape. Since locating the lost ship and setting up a rescue may take longer than the men inside can survive, most submarines are equipped with small chambers that allow a few men at a time to leave the ship and make a free ascent to the surface.
The Navy's answer to difficult or dangerous situations that its people may face is to provide training, and it has proven to be a formula for success. Toward the end of the basic submarine school course, an entire day is spent teaching, demonstrating, and practicing how to conduct an escape from a sunken ship. In addition to learning how to operate the hatches and valves of the escape chamber, the students participate in a physical process that is foreign to anything they have experienced before. They actually leave a flooded compartment and float to the surface.
The practice escapes are conducted from a small airlock that simulates a submarine escape chamber. It is attached to the bottom of a 100-foot high tower filled with water. The Navy divers who run the operation give several minutes of instruction on what is about to happen, then herd some 20 students who are clad in bathing suits and wearing flexible escape hoods into the small metal room. All of the men and one of the divers are crowded together as they would be during a real escape. The trainning chamber has standard submarine hatches (doors) at each end; one leading in from the outside, and the other opening directly into the water near the bottom of the tower.
Once the students are in and settled, the Navy diver inside the airlock makes sure both heavy doors are shut and dogged tight. He then opens the flood valve to let water from the tower come into the chamber. The water comes in with whooshing and squealing noises that drown out anything but shouts. It wells up from the bottom and begins to cover the legs of the students. The air above the water heats up as it is compressed. The rapidly diminishing air space fills with mist that glazes the eye and dims the vision. The students have to move their jaws and swallow to relieve the unrelenting increase in pressure they feel building in their ears.
It takes about five minutes to fill the airlock almost to the ceiling. By the time the pressure inside the chamber equalizes with that at the bottom of the tower, there is just enough of an air pocket at the top of the chamber for the heads of the students. Some of the shorter students can no longer touch the floor - they are held up by the bodies of the taller students.
The diver then undogs and swings open the hatch into the tower. He has the student closest to it put an escape hood over his head. The hood has a clear plastic faceplate through which the student can see. The diver reminds the student to breathe normally (under no circumstances is he to hold his breath, as the now compressed air in his lungs will expand on the way up and cause serious internal damage). The student then reaches down under the water to grasp the coaming at the top of the hatch. He pulls himself down into the water, through the opening, and out into the tower. Once in the depths, the buoyancy of the air in the hood pulls the student slowly up the water column to the surface at the top of the tower. Navy divers in scuba gear are stationed at intervals against the circular wall. They monitor the exercise as the students exit the flooded air lock one by one, and rise passively to the surface, each trailing a stream of expanding air bubbles.
For the students, the ascent is like a near-death experience. They leave the noise, heat, and jostled confusion of the airlock behind as they enter the cool water of the tower. The sides are dark and faint, whereas the surface above is a glowing oval of bright light toward which they float in silence. Periodically an "angel" approaches to check their progress. On reaching the brightly lighted surface at the top of the tower, strong arms reach out and pull them up into the light and air.
Though few men ever need to leave a sunken submarine and float to the surface, all of those who have been through escape training are changed by the experience. They tend to assess new situations in a calm and confident manner. They are more apt to let pressures equalize before taking action; and, they are much less anxious about the transition from one realm into the next.
