MOS 25U: Signal Support Systems Specialist. 25U is responsible for supervising, installing, employing, troubleshooting, and assisting with battlefield signal support systems and networks such as computer systems, local area networks, equipment, terminal devices, power generators, and vehicles. In a combat situation, the 25U is especially crucial to detect enemy signals and jam enemy radio transmissions. In scenarios where large numbers of troops are moving, the Signal Support Systems Specialists