Article 104 – AIDING THE ENEMY
Any person who–
aids, or attempts to aid, the enemy with arms, ammunition, supplies, money, or other things; or without proper authority, knowingly harbors or protects or gives intelligence to or communicates or corresponds with or holds any intercourse with the enemy, either directly or indirectly;
Enemy” is for the purposes of UCMJ defined in Article 99 – Misbehavior Before the Enemy (paragraph – 23c(1)(b)):
Organized forces of the enemy in time of war, any hostile body that our forces may be opposing, such as a rebellious mob or a band of renegades, and includes civilians as well as members of military organizations. "Enemy" is not restricted to the enemy government or its armed forces. All the citizens of one belligerent are enemies of the government and all the citizens of the other.
This is one of the most serious offenses codified within America’s Uniform Code of Military Justice. Hence, it carries a maximum penalty of death, though the Court-Martial or Military Commission may enact a lesser sentence at their discretion.
Aiding The Enemy is one of only 10 crimes under UCMJ that carries the death penalty even when not committed during actual times of war.