The First Polish Corps was formed in the Northwestern region of Russia in the summer of 1917 for subsequent deployment to the front. General Dowbor-Musnicki was appointed commander of the corps. Due to changes in the situation at the front and in Russia, the corps was not sent to the front. In early 1918, the Polish Corps refused to submit to the Soviet government and began taking part in combat operations against the Red Guard on the territory of Belarus. In May 1918, the corps was disarmed and disbanded, and its remaining forces were withdrawn to Poland.
In March 1918, by order of Dowbor-Musnicki, Polish coat-of-arms overprints and inscriptions were applied to stamps of the Russian Empire: "Poczta Pol. Korp." (Post of the Polish Corps) — the first issue. The second issue was produced somewhat later with a modified overprint of the coat-of-arms design and the inscription "Pol. Korp." (without "poczta") and a new denomination at the bottom of the stamp.