Anti-Tank Missile Folder Location
First, we must locate the folder which stores the Anti-Tank Missile(s).

1. Navigate to C:/BF2_Directory/mods/bf2/.
2. Open Objects_Server.zip.
3. Open Weapons/Armament/missiles/.

Anti-Tank Missile Names
Before we begin making modifications, we must know the names of the Anti-Tank Missiles. The names are shown below:

at_predator
eryx

Lock-On Type
Now we will begin modifying the Lock-On Type of the Anti-Tank Missile.

1. Open the at_predator folder.
2. Open at_predator.tweak with Notepad.
3. CTRL + F and type "ObjectTemplate.seek.targetType TTUnique".
4. Change TTUnique after targetType to TTHeat.

This will allow the Anti-Tank Missile to Lock-On to Heat Signatures, which are in Aircraft and Helicopters in BF2.

5. CTRL + F and type "ObjectTemplate.seek.maxDistLock 2000".
6. Change the number (2000) after maxDistLock to 375.
7. CTRL + F and type "ObjectTemplate.seek.reLockTime 0".
8. Change the number (0) after reLockTime to 30.
9. Search for the following lines:

ObjectTemplate.follow.maxYaw 0.5
ObjectTemplate.follow.maxPitch 0.5
ObjectTemplate.follow.changePitch 0.25
ObjectTemplate.follow.changeYaw 0.2
ObjectTemplate.follow.minDist 10

Then change them to:

ObjectTemplate.follow.maxYaw 3
ObjectTemplate.follow.maxPitch 3
ObjectTemplate.follow.changePitch 1
ObjectTemplate.follow.changeYaw 1
ObjectTemplate.follow.minDist 10

10. CTRL + S or File>Save.
11. Close at_predator.tweak.