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 a 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.

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 aliens. 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 this on other levels.

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.