In the 1940s, Boeing engineers recreated atmospheric conditions in the stratosphere at sea level by creating the "Strato-Chamber." The Strato-Chamber was a three-ton tank, 12 feet long by 5 1/2 feet in diameter. The Chamber was fitted with pressure-tight doors on both ends and was divided into two sections, one which replicated airplane cabin conditions and the other, the outside atmosphere. Controls for the Stratochamber were fitted on both the inside and the outside of the chamber, and contact was maintained with occupants through observation windows and a telephone system. The chamber was used to develop new airplane technology that could function at higher altitudes, as well as to familiarize flight crews with the physical effects of high altitude conditions and to learn techniques to counter these effects.