| Prefix |
Country |
|
| A | All to Germany and protectorates | |
| B | All to Great Britain | |
| CAA to CMZ | Not yet assigned | |
| CNA to CNZ | Morocco | |
| COA to CPZ | Chile | |
| CQA to CQZ | Monaco | |
| CRA to CTZ | Portugal and colonies | |
| CUA to CUZ | Not yet assigned | |
| CVA to CVZ | Roumania | |
| CWA to CWZ | Uruguay | |
| CXA to CZZ | Not yet assigned | |
| D | All to Germany and protectorates | |
| EAA to EGZ | Spain and colonies | |
| EHA to EZZ | Not yet assigned | |
| F | All to France and colonies | |
| G | All to Great Britain | |
| HAA to HFZ | Austria-Hungary and Bosnia-Herzegovina | |
| HGA to HHZ | Siam | |
| HIA to HZZ | Not yet assigned | |
| I | All to Italy and colonies | |
| J | All to Japan and possessions | |
| KAA to KCZ | Germany and protectorates | |
| KDA to KZZ | United States | |
| LAA to LHZ | Norway | |
| LIA to LRZ | Argentine Republic | |
| LSA to LWZ | Not yet assigned | |
| LXA to LZZ | Bulgaria | |
| M | All to Great Britain | |
| N | All to the United States | |
| OAA to OFZ | Not yet assigned | |
| OGA to OMZ | Austria-Hungary and Bosnia-Herzegovina | |
| ONA to OTZ | Belgium and colonies | |
| OUA to OZZ | Denmark | |
| PAA to PIZ | Netherlands | |
| PJA to PJM | Curacao (Dutch) | |
| PJN to PJZ | Surinam (Dutch) | |
| PKA to PMZ | Dutch East Indies | |
| PNA to PZZ | Not yet assigned | |
| Q | Reserved for code abbreviations | |
| R | All to Russia | |
| SAA to SMZ | Sweden | |
| SNA to STZ | Brazil | |
| SUA to SUZ | Egypt | |
| SVA to SZZ | Greece | |
| TAA to TMZ | Turkey | |
| TNA to TZZ | Not yet assigned | |
| UAA to UMZ | France and colonies | |
| UNA to UZZ | Austria-Hungary and Bosnia-Herzegovina | |
| VAA to VGZ | Canada (British) | |
| VHA to VKZ | Australian Federation (British) | |
| VLA to VMZ | New Zealand (British) | |
| VNA to VNZ | South African Union (British) | |
| VOA to VOZ | Newfoundland (British) | |
| VPA to VSZ | British colonies not autonomous | |
| VTA to VWZ | British India | |
| VXA to VZZ | Not yet assigned | |
| W | All to the United States | |
| XAA to XCZ | Mexico | |
| XDA to XZZ | Not yet assigned | |
| YAA to YZZ | Not yet assigned | |
| ZAA to ZZZ | Not yet assigned | |