text: Cyberspace Operations and Electromagnetic Warfare Fundamentals
  Electromagnetic Hardening
  2-43. Electromagnetic hardening consists of actions taken to protect personnel, facilities, and/or equipment
  by blanking, filtering, attenuating, grounding, bonding, and/or shielding against undesirable effects of
  electromagnetic energy (JP 3-85). Electromagnetic hardening can protect friendly spectrum-dependent
  devices from the impact of EMI or threat EA such as lasers, high-powered microwave, or electromagnetic
  pulse. An example of electromagnetic hardening includes installing electromagnetic conduit consisting of
  conductive or magnetic materials to shield against undesirable effects of electromagnetic energy.
  Emission Control
  2-44. Emission control is the selective and controlled use of electromagnetic, acoustic, or other emitters to
  optimize command and control capabilities while minimizing, for operations security: a. detection by enemy
  sensors, b. mutual interference among friendly systems, and/or c. enemy interference with the ability to
  execute a military deception plan (JP 3-85). emission control enables OPSEC by—
  * Decreasing detection probability and countering detection range by enemy sensors.
  * Identifying and mitigating EMI among friendly spectrum-dependent devices
  * Identifying enemy EMI that allows execution of military deception planning.
  2-45. Emission control enables electromagnetic masking by integrating intelligence, and EW to adjust
  spectrum management and communications plans. A practical and disciplined emission control plan, in
  conjunction with other EP measures, is a critical aspect of good OPSEC. Refer to ATP 3-13.3 for OPSEC
  techniques at division and below.
  Electromagnetic Masking
  2-46. Electromagnetic masking is the controlled radiation of electromagnetic energy on friendly frequencies
  in a manner to protect the emissions of friendly communications and electronic systems against enemy
  electromagnetic support measures/signals intelligence without significantly degrading the operation of
  friendly systems (JP 3-85). Electromagnetic masking disguises, distorts, or manipulates friendly
  electromagnetic radiation to conceal military operations information or present false perceptions to adversary
  commanders. Electromagnetic masking is an essential component of military deception, OPSEC, and signals
  security.
  Preemptive Countermeasures
  2-47. Countermeasures consist of that form of military science that, by the employment of devices and/or
  techniques, has as its objective the impairment of the operational effectiveness of enemy activity (JP 3-85).
  Countermeasures can be passive (non-radiating or reradiating electromagnetic energy) or active (radiating
  electromagnetic energy) and deployed preemptively or reactively. Preemptive deployment of passive
  countermeasures are precautionary procedures to disrupt an enemy attack in the EMS through the use of
  passive devices such as chaff which reradiates, or the use of radio frequency absorptive material which
  impedes the return of the radio frequency signal.
  Electromagnetic Security
  2-48. Electromagnetic security is the protection resulting from all measures designed to deny unauthorized
  persons information of value that might be derived from their interception and study of noncommunications
  electromagnetic radiation (e.g., radar) (JP 3-85). Changing the modulation and characteristics of
  electromagnetic frequencies used for radars make it difficult for a threat to intercept and study radar signals.
  Wartime Reserve Modes
  2-49. Wartime reserve modes are characteristics and operating procedures of sensor, communications,
  navigation aids, threat recognition, weapons, and countermeasure systems that will contribute to military
  effectiveness if unknown to or misunderstood by opposing commanders before they are used, but could be
  exploited or neutralized if known in advance (JP 3-85). Wartime reserve modes are held deliberately in
  reserve for wartime or emergency use.