- I – Incendiary
- IAFV – infantry armoured fighting vehicle
- IAI – Israel Aircraft Industries
- IAL – Infra-red Aiming Light
- IASD – Instant Ammunition Selection Device
- IBAS – Improved Bradley Acquisition System
- ICC – information co-ordination centre
- ICM – improved conventional munition
- ICM – BB improved conventional munition base bleed
- ICV – Infantry Combat Vehicle
- IDF – Israel Defense Forces
- IDW – Individual Defence Weapon
- IED – Improvised Explosive Device
- IEPG – Independent European Program Group
- IFCS – Improved/Integrated Fire-Control System
- IFF – Identification Friend or Foe
- IFV – infantry fighting vehicle
- IFVwCM – Infantry Fighting Vehicle with Integrated Countermeasures (US)
- IGLS – Individual Grenade Launcher System
- II – image intensification/intensifier
- IIR – Imaging Infra-Red
- ILL – illuminating
- ILMS – Improved Launcher Mechanical System
- ILS – Integrated Logistic Support
- IM – Insensitive Munition(s)
- IMMLC – Improved Medium Mobility Load Carrier
- IMU – Inertial Measurement Unit
- INSAS – Indian Small Arms System
- InSb – Indium-antimonide
- IOC – initial operational capability
- IOF – Indian Ordnance Factory
- IPB – Intelligence Preparation of the Battlefield
- IPF – Initial Production Facility
- IPO – International Programme Office
- IPPD – Integrated Product Process Development
- IR – Infra-Red
- IRBM – Intermediate-range ballistic missile
- IRU – Inertial Reference Unit
- IS – internal security
- ISD – In Service Date
- ISGU – Integrated Sight and Guidance Unit
- ISR – Intelligence Surveillance and Reconnaissance
- ISU – Integrated Sight Unit
- ISV – Internal Security Vehicle
- ITAS – Improved Target Acquisition System
- ITOW – Improved TOW
- ITPIAL – Infra-red Target Pointer/Illuminator/Aiming Laser
- ITT – Invitation To Tender
- ITV – Improved TOW Vehicle (US)
- IVPDL – Inter-Vehicle Positioning and Data Link (US)
- IW – Individual Weapon
- IWS – Improved Weapon System
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