Entertainment technology, such as game engines, can provide low cost operational realism for Military Operations on Urbanized Terrain (MOUT) simulations. However, apart from achieving low cost and high fidelity virtual environments, MOUT simulation systems should also be adaptable with the frequent shifts in operational needs. We found that existing system architectures may not be optimized for reconfiguration with a game engine based approach. To this end, we describe our work on building agile and reconfigurable systems that can construct MOUT virtual environments rapidly with game engines. We propose the Architecture for Rapid Configuration (ARC) to support model interoperability and reusability. Along with ARC, we will explain how two other components, namely Game-based Object Standard Interfaces (GOSI) specifications and the ARC-based Objects Repository (ARCOR), work in tandem with the ARC. In our previous work, we constructed Twilight City, a virtual training environment for MOUT. Our experiences show that the proposed architecture has transformed Twilight City into a rapidly reconfigurable simulation system.