Members of the armed forces who are not hors de combat are taking an “active part”
Hors de combat is not there for padding - its a defined term of the Convention:
A person is hors de combat if:
(a) he is in the power of an adverse Party;
(b) he clearly expresses an intention to surrender; or
(c) he has been rendered unconscious or is otherwise incapacitated by wounds or sickness, and therefore is incapable of defending himself;
provided that in any of these cases he abstains from any hostile act and does not attempt to escape.
A person is not hors de combat simply because they are:
- Sleeping
- Eating
- Unarmed
- Out of uniform
- Defecating
- Fornicating
- Drunk
It also includes people parachuting from a disabled aircraft (but not airborne troops or people abandoning a stricken water vessel). However, once they reach the ground in friendly (to them) territory, they are once again active combatants.