This paper presents the results of the integration of the Deployable Forward Observer/Modular Universal Laser Equipment (DFO/MULE) training system into a multi-service Distributed Interactive Simulation (DIS) evaluation testbed, representing one of the first documented implementations of the Laser Protocol Data Unit (PDU). The DFO/MULE system provides target acquisition and tracking training for Artillery Forward Observers, Naval Gun Fire Spotters, and Forward Air Controllers as well as laser designation and rangefinding training. This stand-alone training system was modified to add a DIS networking capability, allowing ground-based Forward Observers to identify and designate targets for attack by artillery and aviation assets distributed within the Multi-service Distributed Training Testbed (MDTT) network. In addition to providing an overview of the system design and integration approach, this paper explores key issues which directly relate to implementation of the Laser PDU such as laser spot correlation with respect to terrain and targets, laser designation versus laser rangefinding, and laser-guided munitions modeling. The lessons learned from this implementation are discussed, along with suggestions and recommendations for future study and development.