A selective overview of weather-effect studies over the past 20 years, and proposed methods for incorporating weather factors into the force planning and acquisition process. So-called all-weather systems have higher cost and, often, lower effectiveness than simpler systems, and may be stopped by sufficiently bad weather. Force deployment decisions could be tailored to the operational environment, if (1) the weather sensitivities of systems and subsystems were realistically tested at the various stages of development, and (2) sufficient research were done to enable these sensitivities to be translated into gross weather and climate parameters. Military aircraft are tested in nearly perfect weather, while nearly every type of weather in the world can be found somewhere in the United States. Appendixes, coauthored respectively by C. Schutz and R. R. Rapp, document the need for weather sensitivity tests, and present a preliminary mathematical model for including weather factors in force planning.