The Augmented REality Sandtable (ARES) is a research project from the U.S. Army's Natick Soldier Research, Development and Engineering Center (NSRDEC) that is investigating novel techniques for visualizing and interacting with complex battlespace information. The system is being used in collaborative research studies with Department of Defense, academic, and industry partners to provide a Common Operating Picture (COP) at the Point of Need. The ARES architecture was initially developed to support a variety of end user modalities (e.g. physical sand tables augmented with low-cost, commercial technologies; mobile devices; and personal computers). NSRDEC is now expanding the existing architecture to begin investigating user interactions using augmented reality and augmented virtuality (AR/AV) technologies, floor projection of augmented information, and distributed collaboration and telepresence across the various modalities. This AR/AV research also encompasses interaction methods using Commercial Off-The-Shelf tracked controllers (e.g. HTC Vive controller), voice recognition, gesture recognition, and game controllers. Intuitive interfaces across the modalities allow users to create, import, or choose maps and terrains from external data sources; place and move tactical graphics; and interact with models (e.g. line-of-sight, route planning, radio, or CBRN [Chemical, Biological, Radiation, and Nuclear]) in real-time. These approaches offer novel platforms for training and operational planning in Multi-Domain Battlefields. Studied benefits of using the initial ARES prototype already include increased user engagement, decreased cognitive workload, and high utility perceptions. This paper details the modular, Service-Oriented Architecture of ARES. Topics covered include how it provides a COP while conducting expeditionary Mission Command; how it extends the scope of traditional mission planning tools by leveraging models and simulations; and how it allows for third-party application development and integration. It also outlines successful use-cases and provides lessons learned for other system developers.