DIRCM (Directional InfraRed CounterMeasures) is the active, directed defence against IR-guided missiles: a small turret on the platform with a rapidly steerable mirror/telescope and a modulated IR source — nowadays practically always a laser (Continuous wave and pulsed applications, CW/modulated).
The chain works like this (and depends entirely on ESM, EW: Electronic Support Measures):
- the MAWS (Missile Approach Warning System) detects a missile launch and provides the direction;
- within tenths of a second the DIRCM turret slews towards the incoming missile and tracks it with its own fine-tracking sensor;
- the laser illuminates the missile's seeker optics — the very optics that must see the target act as the receiving antenna for the jammer (reciprocity);
- the laser's modulation is matched to the seeker's processing logic: with reticle seekers (Passive homing) it injects false spin-scan/con-scan signals, so that the seeker calculates a large, false pointing error and steers the missile away (optical "inverse gain", Angle deceptive jamming); in the simplest case the detector is saturated/blinded (dazzle).
Strengths:
- Inexhaustible: no cartridges that run out — the laser fires as often as needed; several missiles in succession can be dealt with.
- Works against modern seekers where flares fail (imaging, two-colour): saturating or cluttering the image is always possible, provided enough power reaches the optics.
- Reveals little: the narrow beam (Specific characteristics of laser) can only be seen from the missile.
Limitations: line of sight and weather (laser, Laser rangefinder and laser designator), one target per turret at a time (saturation attacks!), dependence on fast and reliable MAWS cueing (false alarms waste time; missed launches are fatal), and against the very latest seekers with hardening/filters more power or smarter modulation is needed — the familiar cycle. DIRCM now flies on transport aircraft, helicopters and tankers, and increasingly on combat aircraft, as the final element of the package MAWS + flares + manoeuvre.