Curious to explore the undersea world, Alexander the Great used a glass diving bell to submerge himself below the surface. The fish, it is said, “crowded around him in homage.” In 332 BCE, he ordered soldiers to submerge inside diving bells and destroy the enemy’s underwater defenses.

Underwater operations got much more serious in the 1930s when Max Gene Nohl and Edgar End pioneered deep diving to 420 feet in Lake Michigan. Using a hyperbaric chamber in Milwaukee, they demonstrated the ability of a man to spend 27 hours in a chamber at a pressure equivalent of 101 feet of water. They showed that, after several hours, the body becomes saturated with inert gas and remains in balance at that point without harm to the diver. A single decompression successfully ended the session with no adverse effects.

In the 1960s, US Navy Captain George Bond was made principal investigator for the Navy’s Man-in-the-sea program. Sealab I was like an underwater space station with four Navy divers submerged at 192 feet in the Atlantic Ocean near Bermuda. The men worked six hours a day outside the habitat. Sealab II continued the pioneering work in the Pacific Ocean. The former astronaut, Scott Carpenter, spent thirty days underwater. A large hose carried fresh water along with telephone and telegraph connections from the support ship above to the 57-foot-long capsule below.

As divers went deeper and deeper, a serious problem called “high-pressure nervous syndrome" (HPNS) arose. It was characterized by tremors of the hands, arms and torso, along with dizziness, nausea, vomiting, lapses of consciousness and electroencephalographic abnormalities. First described by Peter Bennett, the exact causes (some seem more susceptible than others) are still being sought but, as Bennett predicted, the condition can usually be controlled by adjusting the gas mixtures. Inert gases are ranked according to their narcotic potency in this order (from least to most) helium, neon, hydrogen, nitrogen, argon, krypton and xenon.

Using the knowledge gained over the past sixty years, commercial diving came into its own. Deep-sea saturation divers do salvage operations and work in the oil and gas industry, typically spending two weeks underwater, then a single prolonged decompression, then two weeks on land with the rest of us.

Caption for the photo above: A saturation diver wearing a commercial diving helmet with breathing system, oral-nasal mask, defogger, headlight system, backup breathing gas system, communication system, head cushions, and water ejection system.