Satellite navigation has demonstrated its ability to enhance the safety and efficiency of multi-modal transport systems and act as a stimulant to economic growth and commercial development. The decision of the Transport Ministers to proceed with the definition stage of Galileo currently being funded by the European Commission and the ESA GalileoSat programme will include the complex question of security and defence considerations. Initial studies were completed over the past year in a Civil Military Interface study and by the GNSS Forum for Security and Defence Considerations. This paper presents the findings of the Civil Military Interface study undertaken for the European Commission, DGVII, that identified the security and military implications of a civil operated and controlled satellite navigation service for Europe.