In 1969 off the California coast, a US Navy crane carefully lowered a massive tubular structure into the waters. It was an audacious feat of engineering — a pressurized underwater habitat, designed for an elite group of divers to spend days or even months at a stretch living and working on the ocean floor.Sealab tells the little-known story of the daring program that tested the limits of human endurance and revolutionized undersea exploration.