Numbering about 230,000 at the end of 1945, the WWII Free Polish Forces attached to the British, United States, and other Allied Armed Forces units were permitted to maintain their own Polish Field Post Offices (FPO) within the FPOs of their allies.

The WWII Polish FPO facilities were required to use postage reflecting the nationality of the unit to which the Poles were attached, or the postage available from the different nationalities within these units, the latter primarily being represented by the numerous British Commonwealth participants in the British-commanded units. The postage stamp issues of the United States, Brazil, Norway, Great Britain and the associated British Commonwealth Areas (Australia, British Guiana, Canada, Egypt, India, Jamaica, New Zealand, South Africa, etc.), as well as those of the other Allies, are recorded as being properly applied to correspondence processed through the Polish FPO systems.