| Abbreviation | Definition |
|---|---|
| IRN | Interface Revision Notice |
| IRO | Internal Review Office |
| IRR | Individual Ready Reserve |
| IRR | Integrated Radio Room |
| IRR | Integrated Readiness Report |
| IRR(s) | incidence rate ratio(s) |
| IRS | In Range Shooting |
| IRS | Information and Reconnaissance Ship |
| IRS | Information Reporting System |
| IRS | Interface Requirements Specification |
| IRS | Internal Revenue Service |
| IRSS | Infrared Simulation System |
| IRSS | nfrared Simulation System |
| IRST | Infrared Search and Track |
| IRST | Infrared Search and Track (Capability) |
| IRSTS | Infrared Search and Track Sensor |
| IRSTS | Infrared Search and Track System |
| IRT | Independent Review Team |
| IRT | Initial Response Team |
| IRT | Innovative Readiness Training |