RDG006028 Increased emphasis is being placed on the problem of survival at sea. Currently under evaluation at NMRI are a wet suit for use as a survival garment by helicopter crews and a heated suit for underwater swimmers. Physiological effects of immersion are observed in a 20,000-gallon tank, at water temperatures varying from 75 degrees Fahrenheit down to 28.5 degrees Fahrenheit. In this photograph, a test subject emerges from the tank after two hours of immersion in 40 degrees Fahrenheit water.