This proposal intends to show an innovative and iterative approach to solving the large scale federation interoperability problem. Currently large resources including both time and people (and subsequently, dollars), are required to bring a group of disparate federates (models and simulations) together in a joined/interoperable federation. High Level Architecture (HLA) and other standards have helped in making the sum greater than the individual pieces but there are no tools to insure that the rules of HLA as well as data structure are followed. The process is a manual (document) agreement of federation rules that each federate in turn is required to follow. Only when the federation is brought together are these rules "checked". The automated interoperability test tool in this proposal will aid in capturing these rules in an understandable and databased format. The rules will then be used to execute a test federate using COTS and GOTS products that will allow for automated checking of a proposed federate, one that proposes to join the ultimate federation, against the rules and provide reporting on the proposed federates compliance with those rules. The tool will be scalable to include any federation rules that comply with HLA standards. Benefits It is anticipated that this effort will allow for a reduction in resources (efficiency and cost savings) necessary for developing and testing large scale federations. The initial beneficiary will be the Department of Defense but the tool will be applicable to any large scale federation whether HLA or not. Transportation models (such as those used for traffic control, aviation or automobile) need large scale distributed simulations that will lend itself to this tool. Models or simulations of manufacturing can also benefit by allowing new plant additions (models) to be tested before being federated with existing simulations. Keywords Federation, HLA, Simulation, automation, Federate, Models, interoperability, RTI