Best possible pre-hospital treatment in the event of a mass casualty incident (MCI) is related to prioritizing rescue tasks and using rescue resources efficiently. Currently, in-formation is almost always documented on paper-based forms and communicated by one-to-one talks, messengers, radio and mobile phone. Pervasive computer-based solu-tions are not established yet. Although the mere technologi-cal challenges are on the way of being solved within the near future, questions of usability remain. Concerning this matter, we propose an entangled User Centered System Design (UCSD) and Feature Driven Development (FDD) process and introduce the principle Care & Prepare. It is based on two fundamental assumptions. First, the whole design process has to care for the rescue personnel's' needs in these challenging situations and second, the rescue per-sonnel has to be prepared for using these specialized com-puter applications in case of an MCI. Therefore, daily rou-tine has to be the training foundation for these extraordinary operations.