Austro - Hungarian Post issued special military stamps for use by soldiers of the monarchy.

As Slovenia was a part of the empire, Slovenes serving in the Austro - Hungarian army used military stamps:

First stamp from the left is a Bosnian stamp with overprint 'K.U.K. Feldpost'.

During WW1 most of Slovene soldiers in Austro-Hungarian army were participating in battles with Italy (at Soska front, named by river Soca). Italian army was defeated at that front (in October 1917) and Austrian forces occupied large area of Italy. Overprinted military stamps were used there: