WGBH’s American Experience tells the mostly forgotten story of the US Navy's daring and groundbreaking Sealab program. Divers who attempted to chart the ocean’s depths faced barriers that had thwarted humans for centuries: near total blackness, bone-jarring cold, and intense pressure that could disorient the mind and crush the body. The Sealab “Aquanauts” tested the limits of human endurance and revolutionized our understanding of underseas exploration.

Watch it tonight at 9pm on WGBH 2.