- I/Q — In-phase and Quadrature
- A complex baseband representation of an RF signal using two orthogonal components (cosine and sine). Enables efficient digital modulation, demodulation, and signal processing. The basis of software-defined radio architectures.
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- DiagramTry it: Sar TrainerTry it: Waveform Generator
- IADS — Integrated Air Defense System
- A network of sensors, C2 nodes, and weapons integrated to provide layered air defense. Includes early warning radars, tracking radars, SAMs, fighters, and communication links.
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- IAF — Initial Approach Fix
- The fix that marks the beginning of the initial segment of an instrument approach procedure.
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- IAM — Identity and Access Management
- Framework of policies and technologies ensuring the right users have appropriate access to resources.
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- IAMD — Integrated Air and Missile Defense
- The integration of capabilities to detect, track, and defeat air and missile threats across domains.
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- IAS — Indicated Airspeed
- Airspeed read from the pitot-static system, uncorrected.
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- IATA — International Air Transport Association
- A trade association of the world’s airlines that develops commercial standards and supports airline operations.
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- IBCT — Infantry Brigade Combat Team
- A light brigade combat team built around dismounted infantry for rapid deployment and restrictive terrain.
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- ICAO — International Civil Aviation Organization
- A UN specialized agency that sets international standards and recommended practices for civil aviation.
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- ICBM — Intercontinental Ballistic Missile
- Ballistic missile with range exceeding 5,500 km. Strategic nuclear delivery system with flight times of 25-35 minutes.
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- ICD — Interface Control Document
- A document formally defining the physical, functional, and logical interfaces between systems or subsystems. Critical for integration success in multi-contractor programmes.
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- ICD (JCIDS) — Initial Capabilities Document
- A JCIDS document that describes a capability gap in terms of the functional area, operational tasks, and conditions under which the gap exists. Initiates the acquisition process at Milestone A.
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- ICEYE
- Finnish commercial SAR operator, ~40 X-band satellites in LEO. Sub-metre spotlight, daily revisit. Strong Arctic / disaster-response use.
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- ICMP — Internet Control Message Protocol
- A network-layer protocol used for diagnostics and error reporting, as in ping.
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- ICRF — International Celestial Reference Frame
- The fundamental inertial frame realized by distant radio sources, defining celestial coordinates.
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- ICU — Intensive Care Unit
- A hospital unit providing continuous monitoring and advanced care for critically ill patients.
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- IDF — Indirect Fire
- Artillery, mortars, naval gunfire, and rocket fires delivered without direct line of sight to the target. Indirect fires shape the battlespace, suppress, and destroy at range; commonly used to fix or suppress enemy during breach operations.
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- Diagram
- IDIQ — Indefinite Delivery / Indefinite Quantity
- A US federal contracting vehicle that establishes ceiling pricing and terms for an unspecified quantity of supplies/services to be ordered over a fixed period. Each order is a "task order" under the parent IDIQ. Speeds repeat buys after the initial competition.
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- IDLH — Immediately Dangerous to Life or Health
- An exposure concentration that poses an immediate threat to life or causes irreversible health effects.
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- IDS — Intrusion Detection System
- A network security device or software that monitors network traffic for suspicious activity and known attack patterns, generating alerts when potential threats are detected. Passive monitoring — does not block traffic.
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- IE — Information Environment
- The aggregate of individuals, organizations, and systems that collect, process, and act on information.
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- IEC — International Electrotechnical Commission
- The body that prepares international standards for electrical, electronic, and related technologies.
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- IED — Improvised Explosive Device
- A homemade bomb constructed and deployed in ways other than conventional military use. The dominant threat to dismounted and mounted patrols in recent counterinsurgency operations.
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- IEEE — Institute of Electrical and Electronics Engineers
- The world's largest professional engineering society and a major standards body. Publishes IEEE 802 (LAN/MAN), 1588 (PTP), 754 (floating-point), 802.11 (Wi-Fi), and others foundational to modern computing and communications.
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- IETF — Internet Engineering Task Force
- The standards body that develops and maintains core Internet protocols via RFCs.
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- IF — Intermediate Frequency
- Frequency to which a received signal is shifted for easier filtering and processing in a receiver.
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- IFDL — Intra-Flight Data Link
- A directional, LPI data link exclusive to F-22 Raptor aircraft for intra-flight sensor and track sharing. Uses narrow-beam transmissions to maintain stealth. Cannot communicate with non-F-22 platforms without a gateway (E-11A BACN).
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- IFF — Identification Friend or Foe
- A radio-based interrogation-response system that identifies military platforms as friendly. Mode 5 Level 2 is the current NATO standard with cryptographic authentication to prevent spoofing.
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- IFOV — Instantaneous Field of View
- The angular area seen by a single detector element, setting the ground sample footprint of a pixel.
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- IFR — Instrument Flight Rules
- Regulations governing flight conducted by reference to instruments, typically under air traffic control.
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- IHL — International Humanitarian Law
- The body of international law governing armed conflict (Geneva Conventions, Additional Protocols, Hague Law). Also referred to as the Law of Armed Conflict (LOAC).
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- IIP — Instantaneous Impact Point
- The predicted ground point where a launch vehicle would land if thrust ceased, used for range safety.
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- IL-5 — Impact Level 5 (DoD Cloud)
- DoD Cloud Computing SRG classification for Controlled Unclassified Information (CUI) and mission-critical data up to Mission Criticality Level 3. Requires FedRAMP High + DoD-specific controls and dedicated / virtually isolated infrastructure.
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- IL-6 — Impact Level 6 (DoD Cloud)
- DoD Cloud SRG classification for classified information up to SECRET. Requires a dedicated SIPRNet-connected enclave, cleared personnel, and full Type 1 encryption at rest and in transit. Only a handful of cloud providers are authorised.
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- Diagram
- ILR — Interleaved Radar
- Operation in which a radar interleaves multiple waveforms or modes within a single scan to satisfy competing measurement needs.
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- ILS — Integrated Logistics Support
- A disciplined approach to planning and developing support for a system throughout its lifecycle. Covers maintenance, supply, training, technical data, and facilities.
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- IMA — Integrated Modular Avionics
- Architecture in which multiple avionics functions share common computing resources (processors, memory, I/O) with robust spatial and temporal partitioning. Reduces wiring, weight, and obsolescence churn but increases verification complexity. ARINC 653 defines the partitioning OS interface.
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- Diagram
- Imaging Infrared — IIR
- A missile seeker or surveillance sensor that produces a 2D infrared image rather than a single-pixel detector. Allows target recognition, aim-point selection, and discrimination against flares.
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- IMC — Instrument Meteorological Conditions
- Weather conditions requiring pilots to fly primarily by reference to instruments rather than outside visual cues.
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- IMINT — Imagery Intelligence
- Intelligence derived from visible, infrared, and multispectral imagery collected by satellites, aircraft, or drones. A core collection discipline alongside SIGINT, HUMINT, MASINT, and OSINT.
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- IMO — International Maritime Organization
- The UN agency responsible for the safety, security and environmental performance of shipping.
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- IMP — Integrated Master Plan
- An event-driven plan that documents significant accomplishments, criteria for success, and the relationship between program events, milestones, and technical reviews.
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- Impact Analysis
- A structured assessment of how a proposed change (requirements, design, environment) affects the rest of the system — performance, cost, schedule, risk. The first step of every well-run change-control board review.
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- IMS — Integrated Master Schedule
- A resource-loaded, network schedule that integrates all program tasks, milestones, and deliverables. Contains the critical path and drives program execution.
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- IMU — Inertial Measurement Unit
- A sensor package combining accelerometers and gyroscopes (and sometimes magnetometers) to measure linear acceleration and angular rate. Core component of an inertial navigation system.
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- IMUX — Input Multiplexer
- A filter bank that separates a received satellite uplink into individual transponder channels.
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- In-Stride Breach
- Hasty breach conducted as a continuation of the current manoeuvre — used when the obstacle is encountered with insufficient time for full planning. Requires a 2.5:1 minimum suppression ratio. Contrast with Deliberate Breach.
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- Diagram
- Incident Response
- The structured process of detecting, containing, eradicating, and recovering from security incidents. NIST SP 800-61 defines the canonical phases: preparation, detection/analysis, containment/eradication/recovery, post-incident.
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- Inclination
- The angle between the orbital plane and the equatorial plane, measured at the ascending node. Determines the maximum latitude the ground track reaches (equal to the inclination value).
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- IND — Improvised Nuclear Device
- A crude nuclear weapon fabricated from illicitly obtained fissile material to produce a nuclear yield.
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- Indications and Warning — I&W
- The intelligence discipline of detecting and alerting to impending adversary actions. Relies on known indicators, ambient collection, and analyst pattern recognition to provide decision time.
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- INFOSEC — Information Security
- Protection of information and information systems.
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- Ingress Route
- The planned path a strike package flies to reach the target area, chosen to minimise exposure to detection and engagement. Complemented by the egress route used to depart after weapons release.
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- Diagram
- INS — Inertial Navigation System
- A self-contained navigation system that tracks position and attitude by integrating IMU measurements from a known initial state. Drifts over time and typically aided by GNSS, radio nav, or terrain matching.
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- InSAR — Interferometric SAR
- A technique using phase differences between two or more SAR images to measure surface deformation or create digital elevation models with millimeter-level precision.
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- INSURV — Board of Inspection and Survey
- The board that inspects and certifies the material readiness and fitness of naval ships.
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- Intercept
- The act of engaging and defeating a target — applied to air defence (intercepting an inbound aircraft or missile), comms (intercepting a transmission), or computer security. Context-dependent: same word, very different operational meanings.
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- Interceptor
- A defensive missile or aircraft that engages incoming threats before they reach their target. Examples: PAC-3 vs ballistic missiles, AIM-120 vs aircraft, GBI vs ICBMs, and the THAAD high-altitude interceptor.
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- IO — Information Operations
- The integrated employment of information-related capabilities to influence, disrupt, or usurp adversary decision-making.
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- IOC — Indicator of Compromise
- Observable artifacts such as IP addresses, domain names, file hashes, or network patterns indicating a system has been compromised. Used by SIEM and threat intelligence platforms.
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- IOD — Initial Orbit Determination
- Estimating a first orbit from a short arc of observations to begin tracking a new object.
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- Ion Thruster
- An electric propulsion device ionising propellant (typically xenon) and accelerating ions through an electrostatic grid. Very high Isp (~3,000 s) but millinewton thrust.
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- IOT — In-Orbit Test
- On-orbit verification of a satellite payload and bus before service.
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- IOT&E — Initial Operational Test & Evaluation
- Operational testing conducted by independent test organizations (not the developer) under realistic conditions to determine if a system is operationally effective and suitable for fielding.
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- IOV — In-Orbit Validation
- The on-orbit demonstration confirming a satellite or system meets performance requirements.
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- IP — Internet Protocol
- The network-layer protocol that addresses and routes packets across interconnected networks.
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- IPB — Intelligence Preparation of the Battlefield
- A systematic 4-step process: define environment, describe effects, evaluate threat (ORBAT + doctrine), determine adversary COAs. Produces the threat estimate driving planning.
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- IPE — Individual Protective Equipment
- The mask, suit, gloves, and boots issued to a person for protection against CBRN hazards.
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- IPI — Indigenous Populations and Institutions
- The civilian populace and its institutions considered in the analysis of the operational environment.
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- IPOE — Intelligence Preparation of the Operational Environment
- The joint analytical process of continuously analyzing threats and environments in a specific area.
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- IPS — Intrusion Prevention System
- An active network security system that monitors traffic and can automatically block or prevent detected threats in real time. Sits inline with traffic flow unlike passive IDS.
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- DiagramTry it: Cyber Warfare GuideTry it: Defense Missions Guide
- IPsec — Internet Protocol Security
- A suite that authenticates and encrypts IP packets to secure network communications.
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- IQ — In-phase and Quadrature
- Representation of a signal by two orthogonal components enabling digital modulation and demodulation.
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- IR — Infrared
- Electromagnetic radiation between visible light and microwaves (~700 nm – 1 mm). Sub-bands SWIR, MWIR, and LWIR drive sensor design — MWIR for hot exhaust plumes, LWIR for ambient-temperature imagery, SWIR for haze penetration.
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- IRC — Information-Related Capability
- A tool, technique, or activity used to affect the information environment in support of objectives.
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- IRCM — Infrared Countermeasures
- Techniques and systems that defeat infrared-guided missiles using flares, lamps, or laser energy.
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- Iridium NEXT
- 75-satellite second-generation LEO constellation replacing the original Iridium fleet. 6 planes × 11 satellites + spares at 780 km, 86.4° inclination. Hosts AireonSM ADS-B receivers and Certus L-band broadband.
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- IRS — Inertial Reference System
- A self-contained system using gyroscopes and accelerometers to compute aircraft position, attitude, and velocity.
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- IRST — Infrared Search and Track
- A passive sensor that detects and tracks targets by their infrared emissions without emitting radar energy.
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- IS-IS — Intermediate System to Intermediate System
- A link-state interior gateway routing protocol widely used in large service-provider networks.
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- ISAR — Inverse Synthetic Aperture Radar
- SAR variant imaging a moving target from a stationary sensor.
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- ISB — Intermediate Staging Base
- A temporary secure location used to stage forces and materiel before onward movement into an operational area.
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- ISI — Inter-Symbol Interference
- Distortion where a transmitted symbol smears into adjacent symbols due to channel dispersion.
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- ISIC — Immediate Superior in Command
- The next higher command echelon directly responsible for a ship or unit.
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- ISL — Inter-Satellite Link
- Communication link between satellites, either within the same constellation (intra-plane or inter-plane) or between different constellations. Enables data relay without ground station contact.
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- ISO — International Organization for Standardization
- Independent international standards body publishing ISO 9001 (quality management), ISO 27001 (information security), ISO 14001 (environmental), and thousands more. Member-body model: one national standards organisation per country.
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- Isp — Specific Impulse
- A measure of propulsion efficiency — thrust produced per unit weight of propellant consumed per second (s). Higher Isp means less propellant for the same delta-v.
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- ISR — Intelligence, Surveillance, and Reconnaissance
- Integrated operations and activities supporting commanders' requirements for timely, accurate, and relevant intelligence. Combines sensors, platforms, processing, and dissemination.
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- ISR_CM — ISR Collection Management
- The planning and coordination of sensor tasking to satisfy prioritized intelligence requirements.
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- ISRO — Indian Space Research Organisation
- India's national space agency known for cost-effective missions including Mars Orbiter Mission (Mangalyaan) and Chandrayaan lunar programme. Operates PSLV and GSLV.
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- ISS — International Space Station
- The crewed research laboratory in low Earth orbit operated by an international partnership.
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- ISTAR — Intelligence, Surveillance, Target Acquisition and Reconnaissance
- ISR with explicit target-acquisition function.
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- ITAR — International Traffic in Arms Regulations
- US export control regime governing the transfer of defense-related articles and services, including many satellite technologies. Non-compliance can result in severe penalties.
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- ITRF — International Terrestrial Reference Frame
- A precise Earth-fixed frame realized from geodetic observations, used for high-accuracy positioning.
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- ITU — International Telecommunication Union
- UN specialized agency that coordinates global radio frequency spectrum allocation and satellite orbital positions. Publishes the Radio Regulations governing all satellite services.
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- ITU Band
- International Telecommunication Union designation for radio frequency bands. Standard letter designations (HF, VHF, UHF, SHF, EHF) used globally for spectrum allocation, with NATO/IEEE radar band letters (L, S, C, X, Ku, Ka) for defense applications.
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- ITU Filing
- The regulatory process of registering satellite orbital positions and frequency assignments with the International Telecommunication Union for international protection from interference.
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- ITU-R — ITU Radiocommunication Sector
- The ITU sector responsible for radio-frequency spectrum management and radio standards.
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- ITV — In-Transit Visibility
- The ability to track requisitions and shipments while they move through the distribution pipeline.
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- IUID — Item Unique Identification
- A system of marking assets with a permanent unique identifier for lifecycle tracking.
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- IUSS — Integrated Undersea Surveillance System
- The fixed and mobile acoustic-surveillance network used to detect and track submarines.
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- IWC — Information Warfare Commander
- The warfare commander coordinating electronic warfare, cyber and information operations for a force.
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