The X-EMU project represents the integration development of a fuel cell into a modular traction system for rail vehicles. A universally applicable hardware-in-the-loop (HIL) test environment is being developed for this purpose, in which real components and their models can be integrated, developed further and evaluated. The generally valid findings gained through the research are to be transferred into the development of a modular, scalable traction kit system with fuel cells for integration into the Siemens Mireo® train platform.