High power microwave research requires multiple simulation codes to address physics at different space and time scales. Costs associated with purchase, maintenance and training become important issues when a "toolbox" of codes is needed. Usability issues involving user interface consistency between codes and use of a research community's vocabulary and units are also of concern. Access to source code is of enormous benefit to research groups but is usually not possible within the present technical software market. Along with these "usability" issues, the codes must provide state-of-the-art simulation power. Field Marshal is a simulation environment aimed at addressing the above issues for small research groups involved in electromagnetics design and analysis. Consistent user interface, single-geometry/multiple-tools and inclusion of legacy codes are project goals. A key objective is to construct the environment in such a way that it is usable, maintainable, and extensible by researchers who are not expert programmers. Four primary elements are necessary to cost-effectively achieve this: finite difference techniques, multigrid techniques, a modern scripting environment (e.g. Python), and internet-based distributed development. The role each of these plays in the environment will be outlined. The Field Marshal architecture and key components will be described along with the present state of the environment. Up-to-date information concerning Field Marshal can be found at http://fieldmarshal.org/.