Dr. Richard B. Alley, a geologist and professor of geosciences at Pennslyvania State University, stated this during his narration on the DVD documentary, Earth the Operators' Manual:
"(During the Cold War in the 1950s), the U.S. Air Force needed to understand the Earth's atmosphere for communications and to design heat-seeking missiles. At certain wave lengths, carbon dioxide and water vapor block radiation, so the new missiles could not see very far if they used a wave length that CO2 absorbed. Research at the Air Force Geophysical Laboratory in Hansom Massachusetss produced an immense database with careful measurements of atmospheric gases. Further research by others applied and extended those discoveries clearly showing the heat trapping influences of CO2.
The Air Force did not set out to study global warming, they just wanted their missiles to work. However, physics is physics. The atmosphere does not care if you study it for warring or warming. Adding CO2 turns up the planet's thermostat."
The USAF pioneered research on heat-trapping properties of CO2. "The Air Force didn't set out to study global warming. They just wanted their [heat-seeking] missiles to work."