| CAPT | Captain |
| CB | Confinement to Barracks (punishment) and Counter-Battery |
| CBSO | Counter-Battery Staff Officer |
| CC | Confined to Camp (punishment) |
| CCCC | Cape Colony Cyclist Corps |
| CCD | Commander of Coast Defences |
| CCRA | Corps Commander Royal Artillery |
| CCS | Casualty Clearing Station |
| CDG | Croix De Guerre. (French Gallantry Medal) |
| CDS | Corps Dressing Station |
| CE | Chief Engineer |
| CEF | Canadian Expeditionary Force |
| CEPC | Chief Engineer Port Construction |
| CF | Chaplain to the Forces |
| CFC | Canadian Forestry Commission |
| CGS | Chief of General Staff |
| CHA | Commander Heavy Artillery |
| CHDAVC | Convalescent Horse Depot Army Veterinary Corps |
| CID | Committee of Imperial Defence |
| CIGS | Chief of the Imperial General Staff |
| CLC | Chinese Labour Corps |
| CLLE | Charger-Loading Lee-Enfield rifle |
| CLLM | Charger-Loading Lee-Metford rifle |
| CLRO | Corps Light Railway Officer |
| CME | Chief Mechanical Engineer |