Electronic warfare support measures

thumb|right|[[RAF Menwith Hill, a large ECHELON site in the United Kingdom, and part of the UK-USA Security Agreement.]]

thumb|French ship [[French ship Dupuy de Lôme (A759)|Dupuy de Lôme, specialised in SIGINT]]

In military telecommunications, electronic support (ES) or electronic support measures (ESM) gather intelligence through passive "listening" to electromagnetic radiations of military interest. They are an aspect of electronic warfare involving actions taken under direct control of an operational commander to detect, intercept, identify, locate, record, and/or analyze sources of radiated electromagnetic energy for the purposes of immediate threat recognition (such as warning that fire control radar has locked on a combat vehicle, ship, or aircraft) or longer-term operational planning. Thus, electronic support provides a source of information required for decisions involving electronic protection (EP), electronic attack (EA), avoidance, targeting, and other tactical employment of forces. Electronic support data can be used to produce signals intelligence (SIGINT), communications intelligence (COMINT) and electronics intelligence (ELINT).

Electronic support measures can provide (1) initial detection or knowledge of foreign systems, (2) a library of technical and operational data on foreign systems, and (3) tactical combat information utilizing that library.