Which term refers to undetectable measures in operating procedures to ensure the friendly use of the EM spectrum?

The correct answer is Passive Electronic Protection (EP). This term describes methods and procedures that avoid detection while ensuring the friendly use of the electromagnetic (EM) spectrum. In electronic warfare, passive measures are designed to minimize visibility and vulnerability by simply not emitting signals that can be detected by adversaries. This allows a unit to operate effectively without revealing its position or capabilities, making it a crucial strategy in maintaining an advantage in the electromagnetic spectrum.

Active Electronic Protection, by contrast, involves the active emission of signals or countermeasures which can increase the risk of detection. Electronic Protection is a broader term that encompasses both active and passive measures, but the focus of the question is specifically on undetectable measures, which aligns directly with the definition of Passive Electronic Protection. System Electronic Protection is also a broader concept that refers to protection mechanisms applied at the system level, which may not necessarily prioritize undetectable procedures.

By understanding Passive Electronic Protection, individuals can appreciate the strategies employed to safeguard operations while using the electromagnetic spectrum, ensuring that friendly forces can function without compromising their effectiveness due to exposure to detection.