Which intelligence discipline involves gathering information from electromagnetic emissions?

Signals Intelligence, often abbreviated as SIGINT, is the intelligence discipline that focuses on the collection and analysis of information from electromagnetic emissions. This includes communications between people (like phone calls and emails) as well as non-communication signals (such as radar and other electronic signals). The strength of SIGINT lies in its ability to intercept and interpret these emissions, which can provide critical insights into adversary capabilities and intentions.

Measurement and Signature Intelligence (MASINT) is related but distinct, as it deals with the scientific and technical means of gathering information beyond traditional communications, focusing more on signatures and measurements from various sensors. Human Intelligence (HUMINT) revolves around information gathered from human sources and interactions, which does not involve electromagnetic emissions directly. Open-Source Intelligence (OSINT) pertains to publicly available data and information that can be collected from a variety of sources, including media and publications, rather than through electronic signals.

SIGINT is crucial for modern intelligence since it can yield real-time insights into the activities and communications of potential threats, making it a vital component of national security and military operations.