In this paper, the authors propose to describe the development process of a navigation system, concerning Syntectic Aperture Radar (SAR) applications, starting from the motivation for the sensor selection and finalizing with the first flight-test results. Sensors selection was one of the first steps in the design. Motivations for the accelerometers, gyroscopes, Global Positioning System (GPS) board, magnetometer and all the other hardware components like temperature-sensors selection are explained. A complete description of the hardware integration process, where details like sensors output time synchronization, signal digitalization and calibration are addressed, is given. The developed software is fully explained: starting from the digitalized signals and ending in the flight path outputted by the Iterative Extended Kalman Filter. The developed software includes several features that allow the development of an Inertial Navigation System (INS) focused on SAR applications. The first flight tests have taken place on board of a Cessna Citation II jet aircraft. Results from these flight tests are presented as an evaluation of the performances of the INS.