| J |
| J | Joint Staff (Multi-Service) Numbers/Format same as "G". |
| JAGOS | Joint Air Ground Operations System |
| JAMTO | Joint Airlines Military Traffic Office |
| JCG | Joint Coordination Group |
| JCGRO | Joint Central Graves Registration Office |
| JCRC | Joint Casualty Resolution Center |
| JCS | Joint Chiefs of Staff |
| JCS target | A target appearing on the JCS target list |
| JCSM | Joint Service Commendation Medal |
| JEC | Joint Eradication Committee |
| JEIM | Jet Engine Intermediate Maintenance |
| JFO | Junior Foreign Officer |
| JGS | Joint General Staff (RVNAF) |
| JGS/IG | Joint General Staff/Inspector General |
| JGS/RVNAF | Joint General Staff/Republic of Vietnam Armed Forces |
| JGSIG | Joint General Staff Inspector General |
| JIB | Joint Information Bureau |
| JIC | Joint Information Center |
| Jinking | Constant maneuvering in both the horizontal and vertical planes to present difficult target to enemy defenses by spoiling the tracking solution. Bank, pitch and velocity are all simultaneously changed in this maneuver. |
| JLG | Joint Liaison Group |
| JMA | Junior Military Academy |
| JMA-P | Junior Military Academy - Pleiku |
| JMS-VT | Junior Military School - Vung Tau |
| JOC | Joint Operations Center |
| JOSS | Joint Overseas Switchboard |
| JP | Type of Fuel |
| JP-4 | Aviation Turbine Fuel, Type 4 |
| JPG | Joint US Planning Group |
| JPRC | Joint Personnel Recovery Center |
| JRATA | Joint Research and Test Activity |
| JSCM | Joint Service Commendation Medal |
| JSMB | Joint Services Management Branch |
| JSOP | Joint Strategic Objectives Plan |
| JTACC | Joint Tactical Air Control Center |
| JTD | Joint Table of Distribution |
| JTF | Joint Task Force |
| JTOC | Joint Tactical Operations Center |
| JUMPS | Joint Uniform Military Pay System |
| JUSMAAG | Joint US Military Assistance Advisory Group |
| JUSMAG | Joint United States Military Advisory Group |
| JUSMAGPHIL | Joint US Military Advisory Group Philippines |
| JUSMAGTHAI | Joint US Military Assistance Advisory Group, Thailand |
| JUSPAO | Joint United States Public Affairs Office. Includes United States Information Service, USOM Communications, Media Division, and MACV Psywar elements. |
| JUWTF | Joint Unconventional Warfare Task Force |
| JVREC | Joint Vietnam Regional Exchange Council |
| JWTC | Jungle Warfare Training Center |