As computer systems become increasingly inter-networked, there is a growing class of distributed real-time embedded (DRE) applications that have characteristics and present challenges beyond those of traditional embedded systems. They involve many heterogeneous nodes and links, shared and constrained resources, and are deployed in dynamic environments with changing participants. In this paper, we present a representative DRE application of medium scale that we are developing for the DARPA PCES program. This application consists of several unmanned aerial vehicles, command and control centers, and ground based combat vehicles to perform surveillance, detection, and tracking of time critical targets, an ever increasing threat in today's world. We describe the application, the scenario in which the application is being demonstrated, and issues and challenges associated with developing a DRE application of this complexity.