Electronic warfare (EW) is now considered a branch of information operations, which includes technical measures such as computer security and attacking hostile computers, but also "soft" disciplines such as psychological warfare and deception. Current usage really refers to the entire electromagnetic and acoustic spectra, not just the traditional radio and radar frequencies. It includes passive infrared light heat-seeking guidance and thermal viewing. It includes directed energy from lasers. Indeed, the basic principles are extended against weapons using acoustic energy, principally involving submarines and torpedoes.
Even though current designers of critical civilian systems need to consider the threat, it is hardly a new discipline.  In the Russo-Japanese War of 1905, a Russian captain became aware of a Japanese ship transmitting the Russian position, but was denied permission to jam the signal; the decisive Japanese victory at the Battle of Tsushima Strait might have been prevented had the Russian admiral given permission for EW. Perhaps this can better be described as the first command misunderstanding of the potential value of EW.
EW is often discussed in terms of means and attacks. Effects are produced by the means; the effects may be either permanent ("lethal") or transient ("nonlethal"). The techniques are the means of causing the effects; one distinction, not always clear-cut, is whether they use physical or energy-based methods: a lethal attack can destroy a radar with the blast and fragmentation of a anti-radiation missile, or by an electromagnetic pulse or other high-intensity energy source that burns out, rather than "dazzles", components in the radar. Nonlethal attacks on the same radar could confuse it with physical but passive decoys (e.g., chaff or with active false signals (e.g., deceptive jammers) that do not damage the equipment.
Real-world electronic warfare systems involve integrating a variety of components, as shown in the graphic of a electronic countermeasures suite controller. The controller has multiple ways to interconnect with the devices it controls. Most commonly, in Western EW systems, this is the MIL-STD-1553B bus, but there is an increasing tendency to use commercial-off-the-shelf interconnection technology such as Ethernet-family devices, possibly ruggedized for the military environment. A new trend is to use radio or laser links between the controllers of multiple aircraft in the same formation, in order to refine the location of a threat. Wireless links may also go to ground, satellite, or unmanned aerial vehicle sensors or cooperating electronic attack equipment.
Also connected to the controller, either through a bus or purpose-built interface, is a programming and testing device, such as an AN/ALM-256. Some programming devices can use wide area network (WAN) communications to take new threat and countermeasure information, in real time, from a remote command and control system, and load it into the controller.
- Control: dominate the spectrum, so that friendly forces can gain information on the adversary or attack his systems, and, simultaneously, protect themselves from enemy information-gathering or attack.
- Exploit: use the spectrum to your advantage: detecting the enemy, denying him use of the spectrum, disrupting his C3I-ISR and destroying his resources
- Enhance: use EW as a force multiplier. EW, as part of suppression of enemy air defense, ensures all of one's attack hit their targets, rather than having to send spares because some might be shot down
Electronic warfare has offensive and defensive aspects that work in a “move-countermove” fashion. Often, these aspects are used simultaneously and synergistically to support the mission. In the same way that air superiority allows friendly forces the freedom from attack, freedom to maneuver, and freedom to attack, the proper coordinated use of EW allows friendly forces to use the EM spectrum. As examples, the offensive denial of a command and control (C2) network by jamming disrupts the adversary’s ability to marshal forces that would otherwise engage a friendly strike force. The proper use of EP allows friendly radar and communications to continue operating in the presence of enemy jamming.
Of the five fake landing plans under Plan BODYGUARD deception operations preceding the WWII invasion of Europe, the one the Allies most wanted the Germans to believe FORTITUDE SOUTH, to believe that the main attack would come further north, at the Pais de Calais, the shortest distance across the English Channel. The actual attack at the Battle of Normandy was farther south than the FORTITUDE SOUTH area.
It was to the Allies' advantage to have the shortest ocean crossing to their targets. If they were to land at the FORTITUDE SOUTH area, it would be reasonable to have the invasion force preparing in Kent. They created the fictitious First United States Army Group (FUSAG) under the flamboyant and feared GEN George Patton, and had the U.S. 3103rd Signal Battalion and the British 3118th Signal Service Group created a great deal of radio traffic, coming from locations in Kent. Meanwhile, an absolute minimum of radio traffic came from the real camps in Devon and Dorset in southern England. The dummy radio traffic, the sightings of Patton, and other deceptive information exploited the beliefs of Adolf Hitler, who, for some time after the Normandy landings, insisted they were a fake and held back reserves to use against the "real" invasion. 
Other information operations complement EW. For example, the overall deception plan may use many means to convince the enemy of something untrue, which you want him to believe. One of those means is electromagnetic deception, or the deliberate radiation, reradiation, alteration, suppression, absorption, denial, enhancement, or reflection of EM energy in a manner intended to convey misleading information to an enemy or to enemy EM-dependent weapons, thereby degrading or neutralizing the enemy’s combat capability."  In the FUSAG case, the form of electromagnetic deception was simulative EM deception, or actions to simulate friendly, notional, or actual capabilities to mislead hostile forces. The radio silence at the camps of the real invasion force was manipulative EM deception, or actions to eliminate revealing, or convey misleading, EM telltale indicators could have given German intelligence the knowledge of another large force.
To enhance is to use EW as a force multiplier. Careful integration of EW into air and space operations will detect, deny, disrupt, deceive, or destroy enemy forces in varying degrees to enhance overall mission effectiveness. Through proper control and exploitation of the EM spectrum, EW functions as a force multiplier and improves the likelihood of mission success.
If the enemy used identification-friend-or-foe techniques to recognize his own forces,imitative EM deception' would send the proper "don't kill me" EM signal into enemy systems that imitates enemy emissions.
Techniques of EW
A common distinction breaks EW into three sets of techniques: 
- Learning about an opponent's electronic capabilities, resources and their deployment. At the national/strategic level, this is usually called electronic intelligence, and electronic support (ES) at the tactical level.
- Interfering with the opponent's systems, called either electronic attack (EA) or, traditionally, electronic countermeasures (ECM).
- Minimizing the effects of enemy counteractions on one's own electronics, called electronic counter-countermeasures (ECCM) or electronic protection EP. The latter is a newer and less frequently recognized term.
ES, EA, and EP are preferred terms because, as newer terms, the "E" can be thought of as "electromagnetic" rather than "electronic". This newer thinking helps remember that directed energy and passive sensing are included in the modes.
In Soviet doctrine, EW was called Radio-electronic Combat (REC) [Radioelektronaya Bor'Ba]. They divided it into:
- radio intelligence/intercept, specifically rejecting the U.S. distinction between ELINT and ES
- radio countermeasures (jamming)
- physical suppression/attack
- radio concealment and deception
In each of these sets, purely electronic or computer software/network attacks are called soft kill, while physical destruction of enemy electronic resources is hard kill; there will be countermeasures against both hard and soft kill. Some of the hard kill concerns are general military ones; a tank driving through the building will kill it whether it is the communications center or the cookhouse.
Even with the softer methods, it often is hard to draw the line among the three branches. For example, if an aircraft detects that it is being "painted" by the terminal guidance radar of a surface-to-air missile, the detection being in the electronic support area, the aircraft computer may immediately and automatically respond with jamming (i.e., electronic attack) and launching decoys (i.e., electronic protection). Not to take those immediate steps may mean the airplane is seconds away from becoming a fireball.
Nuances of these distinctions include that EP should not be confused with self-protection. When an aircraft is threatened by heat-seeking air-to-air missiles (AAM), which use the infrared light part of the spectrum, it can release flares for self-protection. The flares are hotter than the engines on which the missile normally homes; they act as decoys. While flares are self-protection, they are not EP, but rather EA against the missiles.
Equipping one's own heat-seeking AAMs with software and electronics to ignore decoy flares is electronic protection of the missile. The flare rejection technique is EP for the missile. It ensures friendly use of the infrared part EMS to track the intended target despite the adversary self-protection/defensive EA actions (i.e., the flare) to prevent or reduce friendly use of the EMS.
While defensive EA actions and EP both protect personnel, facilities, capabilities, and equipment, EP protects from the effects of EA (friendly and/or adversary), while defensive EA is primarily used to protect against lethal attacks by denying adversary use of the EMS to guide and/or trigger weapons. 
- See also: electronic intelligence
In this article, the focus of ES is on tactical warning, of electronic threats against oneself or friendly forces, such that immediate action is necessary. Consider how a radar works: it sends out energy, some of which reflects from the target and is received. It follows, therefore, that if a target is at the very edge of the radar transmitter's range, there may be just enough energy in the beam so that it can be detected, but not enough energy to reflect back a signal that the hostile receiver will recognize.
Against traditional radars, a radar warning receiver can usually detect an enemy radar farther away than the radar can detect the target carrying the warning receiver. With newer low probability of intercept radar, the rules may change; some radars cannot be detected by conventional electronic support receivers.
Directed energy ES
A laser warning receiver (e.g., AN/AAR-47) designed to detect and analyze a laser signal is, in EW terms, ES.  Laser warning presents technical problems different than traditional radio or radar warning: the signal of interest will have have a much smaller beam to intercept. Especially during the day, the signal will coexist with broadband background interference, such as sunlight, or fire or flares at night. New detector and discriminator technologies are needed. 
There will be different requirements for detection of laser rangefinders versus laser designators and laser-beam-riding missiles. 
According to the U.S. joint doctrine, "EA involves the use of EM energy, directed energy, or antiradiation weapons to attack personnel, facilities, or equipment with the intent of degrading, neutralizing, or destroying enemy combat capability and is considered a form of fires." 
The term "fires" has come full circle, to include soft kill as well as hard kill. This definition includes the very hard kill of the AGM-88 HARM anti-radiation missile (ARM), which is a "fast gun" that hits radar very quickly, as opposed to the mixed soft-hard kill of the British BaE Systems ALARM. ALARM will strike a radar if one is active, but, otherwise, it dangles on a parachute over the battlefield, daring a radar to show itself. Either approach denies the enemy the use of radar.
Long after bomber aircraft gave up their aerial gunners, they still needed electronic warfare specialists. When much strategic bombing became the job of fighter-bombers, they needed electronic warfare aircraft, such as the Panavia Tornado ECR, EF-111 and EA-6B Prowler as escorts, with the EF-18 Growler and EW unmanned aerial vehicles (UAV) coming on line, as well as major EW enhancements to multirole aircraft such as the F-22 Raptor.
Directed energy example
A laser or other light source (e.g., xenon arc) designed to blind or disrupt optical sensors is, in EW terms, EA.  Directional infrared countermeasures (DIRCM), such as the AN/AAQ-24, do, however, attempt to blind the guidance seeker of the missile attacking the platform — aircraft or tank — while its function is electronic attack, its goal is self defense. Typically, infrared countermeasures interfere with the final, terminal attack part of a missile trajectory. Directed energy countermeasures, such as the Russian Shtora-1 EOCMDAS (electro-optical counter-measures defensive aids suite) has modes that try to foil the terminal attack (i.e., the final dive into the target) as well as to interfere with midcourse guidance.
Blinding 'must not' be directed at people, but only at equipment. A widely ratified international agreement forbids the use of weapons whose "sole combat function or as one of their combat functions, is to cause permanent blindness to unenhanced vision."  The protocol does not apply to blinding as a collateral effect of other laser-based systems, such as weather instrumentation, rangefinders, etc., but it is a widely accepted principle that unless the device is a true laser weapon intended to kill, it is unwise to give even an incidental blinding capability. After all, the beam could accidentally hit onto friendly forces or civilians.
While an enemy who knew ALARM was in use would be very cautious about bringing up his radars, a deceptive operation in the Gulf War, Poobah's Party (Poobah was the call sign of the EW commander, BG Larry Henry) encouraged the Iraqi air defense to turn on radars. After the defenders were frustrated after the first "invisible" wave from F-117 Nighthawk stealth bombers and hard-to-detect BGM-109 Tomahawk cruise missiles, they finally sensed large numbers of aircraft, and turned on their fire control radars. What they first saw were flocks of drones that showed up brightly on radar. What they saw next were a massive number of anti-radiation missiles from almost every airplane that could carry an AGM-88 HARM.
For many people, jamming brings up an image of high-power, broad-spectrum noise. In the real world, it can be much more complex, if for no other reason that if the frequency(ies) of the threat are known, flooding that frequency will be a more efficient use of the available power. More sophisticated jamming, however, requires more intelligence in the jammer.
In a simplified example of more intelligent jamming, the protection system receives the pulse, sent by the radar transmitter, and repeats it at a higher power level than the real reflection, on the chance that the receiver will assume the weaker but real return is a secondary reflection, and believe the stronger echo, remembering the weak signal and screening it out. Then, on successive pulses, the deceptive jammer would transmit the signal slightly before or slightly after the real return, to give the receiver the impression the target is closer or farther away than its real range.
Self-protection as defensive EA
The AN/ALE-47 Countermeasures Dispenser System [CMDS], is a "smart" electronic warfare expendables dispenser that can integrate with defensive avionics such as radar warning receivers, radar reflector (i.e., chaff) dispensers, radar jammers, as well as helping the pilot with situational awareness of the threat.  Such a dispenser may still get additional control from an electronics countermeasures suite controller such as the Danish-developed AN/ALQ-213.
Meaconing is a specific form of deceptive jamming directed at navigational systems. It will receiving radio beacon, or navigational radar, signals and rebroadcasting them, on the same frequency to confuse navigation. The meaconing stations cause inaccurate bearings to be obtained by aircraft or ground stations. Meaconing also includes deception directed at active navigational aids, which, in normal operation, transmit a response signal on a different frequency than used to trigger the aid. In such cases, meaconing sends out a stronger faked response to confuse other receivers.
Even before the Battle of Britain, in March 1940, British scientific intelligence, under R.V. Jones, became aware of the Luftwaffe setting up navigational aids to direct their bombers over Britain. These were not used significantly during that Battle.
After the Battle, however, a new bombing campaign began, until the Allies invaded the continent and captured the German airfields. During this campaign, there was a constant back-and-forth between the German navigational systems and the British electronic warfare specialists in meaconing those systems.
A good deal of electronic protection (EP) needs to be carried out well in advance of the threat. It focuses on the ensuring friendly use of the [electronagnetic spectrum], such as frequency agility and spread spectrum in a radio, or variable pulse repetition frequency in a radar." These measures keep the enemy from finding the friendly signals to interfere with them.
Procedures to shut down nonessential emanations (EMCON) must be preplanned and the appropriate commands distributed and understood. Operational testers of a new Canadian Forces Situational Awareness System, expressed concern that the EMCON imposed at higher level may prevent lower-level commanders from keeping tactical awareness, unless there are local relaxations for tactical EMCON.
A 2006 comment from the head of the Iranian military electronics sector indicates both the perception of the standards of NATO EP, but that other countries do not intend to have large "kill me" signs on their own equipment. "If our main enemy wants to carry out electronic warfare and jamming operations, our standards are at the NATO level," Ebrahim Mahmoudzadeh, said Iran's radars, passive and active electronic protection "can combat anything that wants to harm us".
Frequency management is the discipline of assigning radio frequencies to functions, units, regions, etc. It includes wartime reserve modes (WARM), an example of which would be a radar frequency never used in training, perhaps with new antennas or transmitters installed just before a combat mission. An obvious use for such modes would be the terminal guidance radar signal for a semi-active radar homing missile, the function of the AN/SPG-62 on AEGIS battle management system equipped ships. Even the existence of WARMs for a particular system will be classified, with the modes themselves even more so.
A filter for equipment, or goggle designed to filter out the harmful wavelength of laser light is, in EW terms, EP. Sunglasses are a trivial form of natural protection against bright light.
Once a military organization commits to EW, there will immediately be conflicts among one's own side, even before direct confrontation with the enemy. The strategic intelligence organizations may want to get national-level information, which puts them against the operational-level organization who want to understand the specific threat confronting them. Once conflict begins, there will still be conflicts, between the ELINT/ES people who want to learn more about enemy capabilities, and the combat operations/EA/EP commanders who want to shut down the enemy systems. There will be concern that EA may affect friendly electromagnetic systems, and the activities will need to be deconflicted.
If the organization is multinational, there will be complex challenges of allowing allies access to sensitive intelligence and EW capabilities. Even when a willingness to share is there, there will be interoperability problems, even among the services of one's own country, then against close allies (e.g., AU/CA/UK/US and NATO), and then ad hoc coalition partners, such as the U.S. and Syria, usually adversaries, allied in the Gulf War.
Intelligence preparation for EW
One of the first conflicts will be between the national/strategic level intelligence collectors and the combat operators. Intelligence will be the foundation for EW planning, starting at the strategic scientific and technical intelligence (STINFO) level of understanding the adversary's basic capability.
Before any operations begin, the strategic ELINT groups will want to do their own information collection, and may ask the combat operations to probe the enemy to trigger his use of signals. "Electronic probing is the intentional radiation into the devices or systems of potential enemies for the purpose of learning the functions and operational capabilities of the devices or systems. Obviously, probing, also called "ferret missions", puts crews, and, if not yet in a war, the peace, at risk.
As conflict grows nearer, electronic warning centers alert friendly forces of impending threats. Detailed ELINT guides the preparation of reprogramming and WARM plans. Eventually, ELINT will blur into ES for specific missions.  Russia, as mentioned previously, does not differentiate between the two. 
On July 24, 1965, an RB-66 electronic warfare aircraft, specifically flying in a warning mode, broadcast the call "Bluebells ringing, bluebells ringing" to a strike mission over North Vietnam. That call was a warning that a fire control radar, for the S-75 Dvina (Western designation: SA-2 GUIDELINE) surface-to-air missile was active. While the U.S. was aware of the presence of SAMs, a civilian Defense Department official John McNaughton, Assistant Secretary of Defense for International Security Affairs, had ruled that the North Vietnamese would not actually use them.
McNaughton's theory was not borne out by reality; the RB-66 broadcast another warning five minutes later, and an F-4C fighter was knocked down by a SAM. While there had been sufficient EW concern to provide warning, the strike force was not prepared to counter the SA-2 threat. Warning alone was not enough.  A specific counter-SAM capability was not ordered until August 13, 1965, and then built from off-the-shelf electronics.  Soon, one of the classic EW dilemmas was seen: jammers interfered with ES receivers.
Planning operational EW
Factors influencing EW planning include available assets; desired effects (exploitation, deception, disruption, or destruction); placement limitations (altitude, range, time, or loads); frequency deconfliction; anticipated EW missions from other Services; and authentication requirements.
It is very easy for jammers to interfere with one's own systems, and, especially in multinational organizations, the planners must emphasize:
- Jammer system design includes directional antennas.
- Capabilities exist to lockout frequencies.
- Friendly forces state realistic restricted frequency requirements.
- A command and control process exists which is responsive to real-time frequency changes.
EW system development
Given the constant challenge-response-counterchallenge nature of EW, some research has suggested that the complexity of electronic warfare systems make it extremely difficult to use standardized acceptance procedures.  Since the starting conditions in which an EW system will have to operate are unpredictable, models using chaos theory may need to be used in planning and evaluation.
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