A field-portable instrument has been developed for the purpose of classifying and identifying chemical agents within munitions by measurement of the linear attenuation property of the agent. For most chemical agents of interest, the gamma-ray linear attenuation coefficient is sufficient to separate the agents by class (nerve, blister, and blood). In addition, many chemical agents of a particular class are separable by the attenuation coefficient. Complications in gamma ray transmission measurements arise due to the packaging of the chemical agents in thick-walled steel containers of various configurations, corrosion, and changes in the state of the material from liquid to solid or gas. Identification of chemical agents within a container and without imaging is contingent upon sampling a region of the container that has a homogeneous distribution of the agent. The instrument allows for several degrees of freedom to accommodate multiple data acquisition protocols, including tomographic imaging. A variety of algorithms have been investigated including single-ray transmission to complete 2D-computed tomography using a collimated isotopic source. Recent results indicate that gamma ray measurements can provide identification of chemical agents in reasonable time frames. This paper will describe the system, data acquisition and processing, and present results from laboratory and field studies.