Removing Turrets
From Halopedia, the Halo wiki
In Halo 3, you can spawn Warthogs, tanks, Prowlers, anything that has a turret, without its turret. The Warthogs in particular look mostly like TT Warthogs.
The steps:
1. Open the menu in Forge, and hover over your vehicle, but DON'T SPAWN IT.
2. Start a new round, not closing the spawn menu.
3. When the screen goes black, but BEFORE the menu disappears, spawn your item.
4. For that round, and no longer, your vehicle will be missing turrets. Non-turret spots are still usable.
Note: Performing with a Mongoose only results in losing the horn. Nothing happens to Ghosts, Choppers, Hornets, and Banshees.