The Mercury space suit (or Navy Mark IV) was a full-body, high-altitude pressure suit originally developed by the B.F. Goodrich Company and the U.S. Navy for pilots of high-altitude fighter aircraft. It is best known for its role as the spacesuit worn by the astronauts of the Project Mercury spaceflights. The MK IV Full Pressure Suit ensemble was also used extensively by the US Navy from about 1959 through the early 1970s in aircraft such as the F-4 Phantom, A-3/A-5/RA-5C Vigilante, and F-8 Crusader. Pre-Mercury development The suit was designed by Russell Colley (who designed and built the high-altitude pressure suit worn by aviator Wiley Post) as a means of providing an Earth-like atmosphere in the unpressurized high-altitude fighter jets developed by the U.S. Air Force and U.S. Navy after the Korean War. The Mark IV suit was first introduced in the late 1950s. Prior to the development of the Mark IV suit, the Navy developed different types of the Mark-series full-pressure suits, but all the suits before the Mark IV had problems with both mobility and weight. The Mark IV suit solved the mobility problems with the use of elastic cord which arrested the "ballooning" of the suit, and at , was the lightest pressure suit developed for military use. The most severe test of the suit occurred during the record-setting balloon flight of Malcolm Ross and Victor Prather in the Strato-Lab V unpressurized gondola to on May 4, 1961. With the advent of pressurized cockpits, and the David Clark Company's contract with the U.S. Air Force and the National Advisory Committee for Aeronautics (later NASA) for a full pressure suit for the X-15 rocket plane, the suit fell out of use. Project Mercury When NASA began the Mercury Project in 1958, one of the first needs was a "space suit": a pressure suit to protect the astronaut in the event of a sudden depressurization of the cabin in the vacuum of space. NASA tested both the Navy Mark IV suit and the X-15 high-altitude suit, and chose the Mark IV because it was less bulky than the David Clark suit, and could be easily modified for the new space role. The Mercury suit incorporated several changes from the Navy Mark IV: Replacement of the "open loop" breathing system with a "closed loop" system, eliminating the rubber diaphragm around the wearer's face. Oxygen entered the suit through a hose