MIL-STD-188-125-2 is the second part of the United States military standard on protection against the electromagnetic pulse of a high altitude nuclear detonation and applies to transportable systems rather than to fixed facilities. The change of scale alters the engineering problem considerably. A fixed facility can be shielded by the construction of the building itself, with welded steel and a dedicated earth electrode system, but a transportable system must be shielded by a shelter that can be moved, assembled in the field and connected to whatever power and communication services are available where it is deployed, so the protection has to be designed into the container and into the interconnection hardware. The standard therefore defines the hardness requirements and the verification approach for this class of system, covering the shelter, the penetrations, the cabling between shelters and the protection of the interfaces with external services, and it addresses the additional difficulty that the installation is not permanent and must be proven to remain effective each time it is deployed.