US Air Force (USAF) SENIOR AIRMAN (SRA) Sidney Crawford, Satellite Communications Technician, 48th Communications Squadron (CS), Royal Air Force (RAF) Lakenheath, England (ENG), replaces a Protocol Data Unit (PDU) back-up battery for a Secure Mobile Anti-Jam Reliable Tactical-Terminal (SMART-T) Satellite, which allows the satellite to transmit and receive secure emergency messages