Defensive Electronic Countermeasures are a subset of Electronic Countermeasures used by attack aircraft to disrupt enemy search and fire control radars.
The video below details the general fucntions, specifications, use and components of the following defensice ECM systems (circa 1962):
The AN/ALQ-35 is a target repeater consists of a tuner, pulse generator, transmitter, and control panel working in concert to display multiple false positives on the enemy’s radar scopes. The unit receives the incoming enemy pulse, amplifies it greatly, repeats it, and sends them back with random delays.
The AN/ALQ-41 and 51 are track breakers are designed to break enemy lock-on and to give false information. It provides simultaneous protection against pulse ranging, FM-CW, conical, and monopulse radar in different ways, based on each method’s angle and range.
The AN/ALQ-51 is a deceptive track breaker to counter S-band fire control radars which employ pulse ranging, frequency modulating carrier wave pulse, and conical scan. It is also designed to cause proximity fuses on the SA-2 SAMs to detonate prematurely or be duded so they did not detonate at all.
The AN/ALQ-55 is comm disrupter that operates in the 100-210MHz band. It distinguishes the threatening enemy communication bands from those of beacons and civilians, evaluates them, and jams them with a signal that’s non-continuous, which helps avoid detection.
The video provides an interesting view on just how advanced ECM in the US Navy was at the time. While in concept the operation of modern systems has changed little over the years, the speed with which modern ECM systems process signals has increased as operating flexibllity over a wider range of frequencies to counter a number of OPFOR IADS.