Instructions
Enter Forge mode from the main menu of "Halo Reach."
Choose a map large enough to accommodate a Scorpion tank, such as "Forge World" or "Highlands." Press "Start Game" to begin.
Press "Up" on the D-pad to enter the Forge creator tool. This switches your character from your Spartan to a floating sphere-like Forge editing tool. As the Forge editing tool, you can fly to any portion of the map. Press the "X" button to bring up the complete listing of objects, weapons and vehicles that can be placed onto the map.
Scroll down to "Vehicles," and then to "Scorpion" to select a tank.
Move the cursor to any point in the level, and press "A" to drop a Scorpion Tank onto the map. You can place up to four Scorpion Tanks in a level while in Forge mode.
Select "Save as new map" to save the Forge settings so that players can enjoy the level with the Scorpion Tank placement preferences that you have configured.