Unarmed Marine

The Unarmed Marine glitch is where the very last Marine in all Pelicans has no weapon, but their hands are in position of wielding an Assault Rifle. When they get out of the Pelican, the rifle appears in their hands. Also, if you manage to save the Scorpion Tank in Metropolis before it gets destroyed by the Scarab, the Marine riding the tank can be seen unarmed.



Halo 2
During the Halo 2 level, Cairo Station, at the part where Johnson and Commander Miranda Keyes and two Marines are fighting off Covenant, you can actually take away a Marine's weapon. First, kill all the Covenant. Then, when a Marine fires his SMG at a body, swap weapons with him (it works best if you have a M6C Magnum). With luck, the Marine won't pick up the pistol and will run around without a weapon. It is possible to do this on other levels. Also, If you have say, an SMG as a secondary weapon and a pistol as a primary weapon, and trade the pistol for a marine's SMG, he will not recieve the pistol and the marine will drop the SMG and be unarmed. This is rare and is best done on Cairo Station.

Halo 3
It is also possible, sometimes in the Halo 3 level, Sierra 117. However, it only works with Gunnery Sergeant Pete Stacker. It is only possible to do this with a Pistol and Spiker.

Trivia

 * An unarmed Marine is also seen in Halo: Combat Evolved, and has the same skin as Mendoza.