| M/V | Motor Vessel |
| MAC | Motor Ambulance Convoy |
| MAJ | Major |
| MB | Medical Board |
| MC | MIlitary Cross |
| MDS | Main Dressing Station |
| MEF | Mediterranean Expeditionary Force |
| MFD | Military Forwarding Department |
| MFO | Military Forwarding Officer |
| MFP | Military Foot Police |
| MGC | Machine Gun Corp |
| MGGS | Major General General Staff |
| MGO | Master-General of the Ordnance |
| MGRA | Major General Royal Artillery |
| MGS | Machine Gun School |
| MIA | Missing in Action |
| MID | Mentioned in Dispatches |
| MLO | Military Landing Officer |
| MM | Merchant Marine |
| MM & Bar | Military Medal awarded twice |
| MMGC | Motor Machine Gun Corps |
| MML | Manual of Military Law |
| MMP | Military Mounted Police |
| MPI | Mean Point of Impact |
| MPSC | Military Police Staff Corps |