Question came to me when reading about the policy of pals battalions. What struck me was that obviously a lot of these conscripts would have been poor and ordinarily unable to afford a passport. Did governments put in place a scheme were visas/passports for their soldiers or when you traveled with the armed forces, did it just not matter?
While forces especially today do pay for members relocation costs, especially when dependents are involved or it is from one long term posting to another, civilian travel documents beyond their military ID are another matter.
When deploying to combat zones it's exceedingly rare for arriving troops to go through customs thus eliminating the need for most documents.