This presentation discusses the lessons learned using COTS products on the United States Coast Guard’s Nationwide Differential Global Positioning System (NDGPS). The Coast Guard manages a NDGPS for the United States Department of Homeland Security, where the system is required to provide accuracy within 3-meters and 99.7% system signal availability. Due to the environment, most of the COTS products evaluated and selected for the system were pushed beyond their design limits. This pushed the development team to develop creative and innovative solutions to overcome the challenges. The NDGPS was a very challenging engineering project that combined an Online Transaction Processing (OLTP) environment with a graphical user interface, which required real-time updates. It also incorporated the storage of operational data with archive data, which allowed users to run data analysis on the same hardware as the operational software. While this is not a desired state, it allowed the fielding of a system in a very short period of time that met initial customer requirements. A spiral software development approach will be used to evolve the system to the desired state over the next few years.