The Quest Joint Airlock was delivered to the ISS by STS-104 and installed onto the Unity module. In a series of spacewalks the astronauts moved the oxygen and nitrogen tanks onto the airlock exterior. The six metric ton Airlock consisted of two cylinders of four meters diameter and a total length six meters. The Airlock could be pressurized by the externally-mounted high pressure oxygen-nitrogen tanks, and was to be the sole unit through which all future EVAs were to take place. (Until that point, all EVA entries/exits had been through a Russian module in ISS, with non-Russians having to wear Russian space suits).