The U.S. Army Corps of Engineers (USACE) owns and operates seventy-five (75) powerhouses in the continental United States. The facilities are ultimately owned by Department of Defense (DoD) through the Department of the Army. Most of these powerhouse facilities contain both water-based and CO2-based fire protection systems that were installed during original facility construction, largely occurring from 1940 through 1980. Federal powerhouse facilities utilize congressionally appropriated funds for the minimal facility operation and maintenance. The vast number of equipment, systems, and components contained in each powerhouses requires continual maintenance, replacement, and upgrade. New technologies have evolved to the point that newer systems are beginning to replace existing systems. The existing fire protection systems of most USACE facilities have been in service greater than 25 years. As such, the Hydroelectric Design Center (HDC) of USACE has revised fire protection requirements in order to allow new technologies to be installed in order to provide reliable, relevant, and maintainable replacement or upgraded fire protection systems. Typical fire hazards of the powerhouse include the Generator Enclosures, Oil Storage & Oil Purification Rooms, Flammable Storage Rooms, Indoor (Station Service) transformer vaults, and Exterior distribution or general step-up (GSU) transformers. All of these hazards are typically protected by high pressure CO2 fire protection systems except the Indoor [Station Service] Transformer Vaults and Outdoor [GSU] Transformers and Outdoor Oil Insulated Breakers which are protected by water spray fire protection systems. Several plants have undergone or are undergoing renovation of their original high pressure CO2 based fire protection systems. Where the existing high pressure system is not replaced in kind it is being replaced by either a low pressure CO2 system or a clean agent total flooding system replacement. This presentation will outline the major equipment changes, the system trade-offs in performance and cost, the installation and outages, along with the maintenance needs and ancillary equipment affected in the powerhouse. Installation details will be presented for several new water mist system s installed in both flammable and oil storage rooms and oil filtration rooms. The replacement of an existing hydroelectric generator high pressure CO2 system with a clean agent system will also be illustrated.