| Abbreviation | Definition |
|---|---|
| IR&D | Independent Research and Development |
| IR&D | International Research and Development |
| IR/MM | Infrared/Millimeter |
| IR/MMW | Infrared/Millimeter Wave |
| IR/RF | Infrared/Radio Frequency |
| IR/VIS | Infrared/Visible |
| IRA | Irish Republican Army |
| IRA | Irish Repuplican Army |
| IRA | Provisional Irish Republican Army |
| IRAC | Interdepartment Radio Advisory Committee |
| IRAD | ndependent Research and Development |
| IRAMS | Improvised Rocket-Assisted Munitions |
| IRAMS | Instrument for Reflectometry Analysis of Moisture in Soils |
| IRAPT | Invoicing, Receipt, Acceptance and Property Transfer |
| IRB | Improved Ribbon Bridge |
| IRB | Initial Ready Brigade |
| IRB | Interface Requirements Board |
| IRBM | Intermediate Range Ballast Missile |
| IRBM | Intermediate Range Ballistic Missile |
| IRBM | Inter-mediate Range Ballistic Missile |