I'm not a scientist, but I feel confident about this statement: Humans require oxygen to live. The thing is, we don't necessarily need the oxygen to come from air, though that is how our lungs are designed to receive it.
When submerging underwater for extended periods of time, humans have devised ways to bring oxygen with us so we don't drown and stuff, but there's a problem. Breathing air while under the enormous pressure of deep water makes nitrogen in our bodies dissolve, creating air pockets in the blood and organs and causing decompression sickness.
Retired heart and lung surgeon and inventor Arnold Lange has a solution: liquid breathing.
Lange has a number of patents for designs that would allow a human to essentially breathe like a fish. His scuba suit would allow a human to breathe "liquid air" made of a formula that has been highly enriched with oxygen molecules.
Lange's inventions would allow divers to descend to deeper water depths without getting the bends.
This isn't a new concept. In the medical field, liquid ventilation is used for premature infants, whose lungs haven't developed to safely transition from the liquid environment of the womb.
Navy SEALs reportedly experimented with liquid ventilation in the 1980s, and the need for safe evacuations from submarines has been a high priority ever since men submerged ships. Today, the U.S. Navy recruits deep sea divers for search and rescue missions, diving salvage operations, and even performing ship maintenance.
Liquid breathing is by no means a perfected science (and not just because in order to dispose of the CO2 humans normally exhale, deep water liquid breathing requires an artificial gill in the femoral artery *shudder*), but its medical — and military — applications urge scientists on.