United States of America
Practice Relating to Rule 4. Definition of Armed Forces
The US Field Manual (1956) and Air Force Pamphlet (1976) define armed forces with reference to Article 4(A) of the 1949 Geneva Convention III.
The US Naval Handbook (1995) states that combatants
include all members of the regularly organized armed forces of a party to the conflict … as well as irregular forces who are under responsible command and subject to internal military discipline, carry their arms openly, and otherwise distinguish themselves clearly from the civilian population.