Turretless vehicle glitch
From Halopedia, the Halo wiki
The Turretless Vehicle Glitch can only be done in Forge Mode of Halo 3. This glitch has several different effects on different vehicles, mostly removing the onboard armaments. If it were to be done on the Warthog, the Brute Prowler or the Scorpion, it will remove the turrets/cannon. If done on the Wraith, it removes the large section of the body where the Plasma Mortar are. Also note that on both Scorpion and Wraith, it will remove the secondary turret. If the glitch is to be done on other vehicles such as the Chopper, the Ghost, the Banshee and the Hornet, it will remove the cannons, making it incapable of attacking. However, if a person drives one of the vehicles mentioned above, they would be able to see the cannoncs being fired but no one else can and the shots would do no damage. The glitch also makes the Mongoose unable to honk it's horn.
When you perform this glitch, the vehicle is still drivable (except the turret position). However, the only consequences are that the vehicles would be defenseless due to removal of their armaments.
How to
The ability to do this glitch may have something to do with the number of people in the party. It doesn't appear to work with only one person in the party because the spawn vehicle screen/menu disappears when you start the new round. Performing this glitch successfully seems to rely on the connection you have because if your connection is too good, the menu disappears but if the connection isn't perfect or has a slight bit of lag, it works.
To perform this glitch you must be in a forge game. Once in Forge, enter Forge/Monitor mode and bring up the vehicle spawn menu by pressing 'X'. When the menu is up get the party leader to start a new round. Just after 'Round Over' is heard, the screen blacks out. The menu will stay up for several seconds after the "round over". As soon as the screen goes completely black, spawn the vehicle you want to make turret-less. When the new round has started, go to the spot that you were previously standing. The turretless vehicle you want should be in the spot you were. The vehicle will only remain in its turret-less state for that particular round.
If you start a new round, end the game or save the map with the turret-less vehicle and load it again in forge or a custom game the vehicle will be in its normal state. NOTE: You must spawn the vehicle immediately once the screen is totally black because if you spawn it while you can still see it won’t be turret-less and if you wait too long the menu will disappear. This glitch is relatively easy once you know how to do it. Also sometimes when you start the new round the menu disappears and you can’t spawn the vehicle.
