The Fusion Reactor acts as the main source of energy for the United States of America. Many of these are built in American bases, and they can be upgraded with control rods to double their power output.
The technical specifications and detailed plans of the many Cold Fusion Reactors used by the United States to power their frontline bases are hidden files and documents that no standard person is allowed to see. However, the plans got out during the Global War on Terror when countless Cold Fusion installations were left behind in Europe after the US retreated. It was revealed to be little more than hubs where power is gathered from large, regular fusion reactors back in permanent US settlements. The R&D Dept. had named them Cold Fusion to spice up the United States research teams and bring them better PR, but since the reveal of the technology inside, they are simply referred to as Fusion Reactors today.