After drinking the strongest, most foul-tasting coffee I had ever experienced, we were led below decks to the decompression chamber.

We gathered around one of the strangest-looking contraptions I’d ever seen. First the Mark V rig—and now this. After years of snorkeling along with my surfing, it was becoming clear that surviving while you worked underwater was a lot more complicated than I had ever imagined.

Five of us at a time would enter the chamber with an instructor. When the heavy round door swung shut behind us, the space suddenly felt a lot smaller.

Inside, we would be taken down to a simulated depth of 300 feet while breathing pure oxygen—a test designed to see how our bodies reacted to oxygen toxicity under pressure. The instructors were watching closely for signs of Central Nervous System (CNS) oxygen toxicity—twitching, tunnel vision, nausea, confusion, or anything else that suggested our nervous systems were beginning to misfire.

Each of us was handed a washer and told to hold it between our fingers and thumb. If we dropped it, they wanted to know about it.

The chamber test wasn’t just physical—it was psychological. They wanted to see how we handled being confined in a tight, uncomfortable space, whether we could stay calm, recognize symptoms, and communicate problems quickly. If someone panicked in a chamber, chances were he would panic underwater.

The Petty Officer then pulled out a balloon and said he had a couple of “show-and-tells” to demonstrate what could happen to our lungs when we dove. He inflated a red balloon and tied it off, then pointed to a soup can hanging from a string.

As the pressure in the chamber increased, the sides of the can slowly began to cave in while the red balloon began to shrink—a simple but effective demonstration of what happens to trapped air as you descend.

“We’ll come back to this when we get to three hundred feet.”

By the time we reached the simulated depth, the balloon had shriveled to the size of a prune. He then pulled out a second balloon—blue this time—and blew into it, inflating it to full capacity.

“Think of this as your lungs when you take a breath of compressed air at depth,” he said. “When you ascend back to the surface, it will expand.”

He held it up so we could all see it. “And so will your lungs.”

He let that settle before finishing the thought.

“Which means you better be exhaling all the way up.”

Then he added one more warning, explaining that if we ever had to exit a submarine, we would be exhaling all the way to the surface. But even in the pool, holding your breath on ascent could cause an embolism.

“So be extra careful during pool training. If you run out of air or leave your tanks on the bottom—exhale all the way to the surface.”

Point made.

But what was that he was saying about a submarine?

READ MORE WAR STORIES @ . . .