All the preceding chapters described how sensors and weapons use the electromagnetic spectrum. Electronic Warfare (EW) is the military fight over that use itself: denying the spectrum to the opponent, and securing it for your own use.
The common (NATO) definition:
Electronic Warfare is military action that uses electromagnetic energy to exploit the electromagnetic spectrum, to deny or reduce the opponent's effective use of it, and to protect one's own use of it.
Three verbs are hidden in that definition, and they form exactly the three-way division of the field (The three parts of Electronic Warfare):
- Exploit — listening to the spectrum to gain information: who is transmitting, where, and what does it mean? (ESM)
- Deny / attack — actively disrupting, deceiving or neutralising the opponent's use of the spectrum. (ECM)
- Protect — making sure your own sensors and links keep working despite the other side's ECM. (EPM)
Why this is a separate field follows directly from the earlier chapters: the entire fire control sequence (Executing the fire control sequence using the EMS) and almost every guidance method (Missile Guidance) rely on the EMS. Whoever loses the spectrum is blind, deaf and mute at the same time — radars see nothing, links drop out, weapons miss. That is why modern conflicts almost always begin with the fight for the spectrum.
In older (and much Dutch) literature the three pillars are called ECM, EPM and ESM — this course material follows that division. In current NATO/US doctrine the same functions are called Electronic Attack (EA), Electronic Protection (EP) and Electronic [Warfare] Support (ES). The content is the same; only the labels differ.