[SW6906]

My understanding is that "soldiers" caught fighting wearing civilian clothes are subject to immediate execution.

[mewzilla]

... "soldiers" caught fighting wearing civilian clothes are subject to immediate execution.

That's what I thought.

[ONA-ASIS]

I taught a part of the Laws of Armed Conflict (essentially the GC) at the Royal Australian Naval College and yes, combatants in civilian clothing are afforded no protection under the GC and can be executed on the spot (if that is the law of the capturing country). Ditto enemy combatants disguised as friendly troops.