The purpose of this study was to solve the design and development problems critical to the construction of a spectrally scanning CO2 gas laser for chemical agent detection for airfield defense. The spectrally scanning CO2 gas laser is an active spectrometer that samples the infrared transmission of the atmosphere over a one to ten mile path at several wavelengths in order to detect the presence of chemical agents in that path. A high-speed three-to-eight wavelength computer program was generated. Computer runs were made comparing the sensitivity of the system to various agent interferent combinations for four and more wavelengths. A four wavelengths system was selected to detect the specified agents to the required sensitivity and reject the specified interferents. A four-wavelength scanner and modulator was designed and constructed to generate in rapid sequence the four wavelengths selected under the spectral tuning techniques investigation. Studies were carried out of the cavity optical configuration to optimize stability, higher order mode rejection, diffraction losses, Fabry-Perot interference, gain, and power output while maintaining an effective cavity path length exceeding twenty feet. A ten-pass folded system was designed and fabricated that met the requirements needed to obtain the specified performance. Power output and gain measurements were made on two separate, sealed, isotopic CO2 laser systems.