Very true

We were allied with Russia in the Second World War.

Correct. That would be the fourth Geneva Conventions that would outline treatment of non-uniformed combatants. I was holding them to a higher standard than I should have. The term partisan was thrown a lot during the war and the use of non uniformed combatants was usually met as a sign of underhanded warfare and partisans were usually executed on site. The fourth Geneva Conventions have been troublesome in regards to combatants in informal attire and treatment of prisoners of war since then.

Not fighting in uniform… a clear violation of the Geneva Conventions. That meant the plainclothes guy was commonly executed if captured.