Commander Operational Test and Evaluation Force (COMOPTEVFOR) leveraged a Distributed Engineering Plant (DEP) test event to provide data supporting joint interoperability assessment in an Operational Assessment (OA) of the Next Generation Command and Control Processor (NGC2P). Interoperability metrics cued root-cause discovery of a serious interoperability issue. DEP is a useful tool supporting interoperability testing of major combat systems and their ancillary equipment in a joint environment.