Interoperability is headline news in the computer industry today. Companies spend millions to enable computer systems to "talk" to each other. Industry leaders like Hewlitt-Packard, Motorola and British Petroleum are opting for common software approaches or common operating environments (COE for short) to solve interoperability problems. Why? The most common answer given is that while interoperability is critical, interoperability must be affordable. While industry is spending money, the government is spending time studying the problem in many task forces and blue ribbon panels. The recently completed Defense Science Board Report on Open Systems (Open Systems Task Force, October 1998) coined the term "Plug and Fight", analogous to industry's "Plug and Play", to capture the essence of the future capability DoD must have: systems that are modular, interchangeable, and interoperable. DoD's Command, Control, Communication, Computer, and Intelligence (C41) For the Warrior (C4IFTW) vision has been stated as follows: "The Warrior needs a fused, real-time, true-picture of the battlespace and the ability to order, respond, and coordinate vertically and horizontally to the degree necessary to prosecute the mission in that battlespace. " [OSTF 1998] Clearly this Holy Grail of capabilities encompasses more than just C41 systems. Tactical weapon platforms and other embedded computing systems must also play a significant role in the Plug and Fight operational forces vision. The U.S. Army Digital Battlefield Concept is an example of "Plug and Fight" technology for Army maneuver forces. The digital battlefield concept is most easily described as an overall heightened state of situational awareness for operational elements on the battlefield. Most would agree that the digital battlefield requires an unprecedented level of interoperability between systems that historically had no interoperable requirements at all. The notion of a COE for weapon platforms, a real time COE or RT COE, has been advanced by many as a potential solution to attain interoperability on the digital battlefield. The Army's Weapon System Technical Architecture Working Group (WSTAWG) is currently focused on developing an RT COE concept for Army weapon platforms. All this conceptual development will be moot if the capability is not affordable. Affordable for the purposes of this paper refers to the ownership costs associated with the development and maintenance of the weapon system software. It has been estimated that software maintenance accounts for about seventy percent of a weapon system' s overall IT life cycle cost. Of that cost approximately seventy-five percent is tied up in analysis and testing of post deployment software. Considering the number of systems, and their software/interoperability complexity, involved in the Army's Digital Battlefield, there should be plenty of employment for software engineers of the next century! It is the premise of this paper that affordable software for weapon platforms can be built using an RT COE concept that meets warfighting requirements for interoperability with the additional benefits of modularity and interchangeability. The Defense Information Infrastructure Common Operating Environment (DII COE) originated in 1995 with a simple observation about command and control systems: certain functions (mapping, track management, communication interfaces, etc.) are so fundamental that they are required for virtually every command and control system. Yet these functions are built over and over again in incompatible ways even when the requirements are the same, or vary only slightly, between systems. If these common functions could be extracted, implemented as a set of extensible low-level building blocks, and made readily available to system designers, development schedules could be accelerated and substantial savings could be achieved through software reuse. Moreover, interoperability would be significantly improved because common software is used across systems for common functions, and the functional capability only needs to be built correctly once rather than over and over again for each project. These observations led to the development of the present DII COE. Although its roots are in the C41 arena, the DII COE and its basic principles are not unique to DoD C41 systems. It has been recognized from the outset of the Army's IT initiatives that common software could play a key role in the integration of weapon platforms into the digital battlefield. There continues to be lively debate over the exact role of common software for the embedded computing environments of tactical weapon platforms. The arguments and issues are complex, spanning the spectrum of operations, technology, business and politics. What is needed is a demonstration of common software for embedded so that the real issues can be evaluated. This paper describes a concept for developing a COE for the embedded computing environments of Army weapon platforms.