The provision of Embedded Training (ET) capabilities is written in the requirements documents for future manned ground fighting vehicles as well as for upgrades to current force fighting vehicles including the Stryker, the Abrams and in the Marine Expeditionary Fighting Vehicle (EFV). ET allows vehicle crew members to train anywhere, anytime. Manned Ground Vehicles (MGV) crewmen use optical vision blocks as a safe means to see the world outside. This paper describes an electro-optical Switchable Vision Block (SVB) that not only allows the crew to see the world outside, but also serves as a visual interface to virtual environments for embedded training. Other components for embedded training systems are already in place, including collective simulation systems like CCTT and “drive by wire” systems that allow soldiers to use the vehicle controls either for operations or for training. The SVB is the missing link between current and evolving simulation-based training systems and the soldier. This paper describes the design and development of SVB prototype technology. Three prototypes were created that represent tradeoffs for the multi-dimensional design space. The key challenges for this design were the integration of an optical out-the-window view with high-resolution, collimated views of virtual environments in a way that: Did not degrade operational performance, including transmissivity for the optical view and luminance for the virtual view, Met form and fit restrictions representative of future and current force vehicles Met stringent weight and overall size restrictions Provided a fail-safe configuration that ensured a working optical path view for the full range of failure modes, including ballistic integrity.