MIL-STD-188-125-1 establishes minimum requirements and design objectives for high-altitude electromagnetic pulse (HEMP) hardening of fixed ground-based facilities that perform critical, time-urgent command, control, communications, computer, and intelligence (C4I) missions. The standard prescribes minimum performance requirements for low-risk protection from mission-aborting damage or upset due to HEMP environments. It also addresses minimum testing requirements for demonstrating that prescribed performance has been achieved and for verifying that the installed protection subsystem provides the operationally required hardness for the completed facility. Covered fixed ground-based facility types include subscriber terminals and data processing centers, transmitting and receiving communications stations, and relay facilities. Use of the standard for HEMP protection of other ground-based communications-electronics facilities that require HEMP hardening is also encouraged. The standard applies to both new construction and retrofit of existing facilities. Only local portions of facility interconnects are addressed. The standard implicitly assumes that survivable long-haul communications paths, fiber optic links, or other hardened interconnects between facilities will be provided as required for mission accomplishment. Uniform application of MIL-STD-188-125-1 requirements ensures balanced HEMP hardening for all critical facilities in a network.