A basic defensive structure, the wall is specifically meant to stop opposing units dead in their tracks. It will essentially delay the enemy from advancing, while your units can attack them from behind your wall if they’re within range.
Machine Gun Nest
The Machine Gun Nest is the basic anti-infantry defensive structure. Manned by one GDI soldier, the Machine gun nest will mow down infantry, but is susceptible to enemy machine gun fire. A few of these placed side by side will create a huge threat. They can also defend against incoming aircraft.
Predators are capable of moving back and forth on the battlefield, and they are a strong defense against incoming vehicles. Good luck getting anything past more than one of these guys.
The Missile Squad has two functions as a defensive unit. The first one is to defend against enemy aircraft. They will actively move left and right to defend from air attacks. The second function is to defend against incoming vehicles. While not as effective, they still have a strong assault against vehicles on the ground.
The Anti-Tank Barrier won’t stop vehicles, but they’ll certainly slow them down while imposing a significant amount of damage. You’re best off sending in infantry to destroy these before sending in your main units.
Like the Anti-Tank Barrier, the Barbwire will instead slow infantry, but all while causing significant damage. You’ll probably see a few men stuck in the wire while the rest of the attacking force is already moving on, assuming they even made it past that point.
The guardian is a mobile form of the Machine Gun Nest. It is capable of mowing down incoming infantry, while at the same time, it has a reasonable attack force against incoming air attacks.
The Guardian Cannon is a decently sized cannon meant for defending against incoming vehicles. It does a great job at it, too. It is weak against infantry, and can’t attack air units.
The Rifle Squad is slightly more expensive in this case, as it is a stronger defensive unit, capable of defending your base from land and air attacks. This unit is strong against infantry and will actively move across your defensive line to protect from soldiers on the field.
The Pitbull is a mobile version of the Missile Squad. It will actively move across your defensive line to deal with incoming air units, while at the same time, it will actively defend against any vehicles that stand in its way.
Similar to being on the offense, the Sniper team is a unit capable of staying far back on the battlefield while still being able to eliminate any incoming infantry with great ease. If you’re looking for a good infantry defense, this is the unit for you.
Flak will protect your base from any and all incoming air units. It’s got a bit of power, too, so this structure, while expensive, will easily cover for a number of cheaper anti-air units.
The Zone Trooper is a strong infantry capable of defending from enemy tanks and infantry all alike. A couple of these in well placed positions (behind walls) will give you a good armored defense for your base.
The Watch Tower is the most powerful anti-infantry defense at your disposal. It requires a minimum range to be effective, but with power like this, you don’t have to worry too much about infantry getting too close.
Like the Watch Tower, this is the most powerful anti-vehicle defense in your inventory. It too needs minimum range to attack, but any vehicle that comes within its aim is likely to be destroyed very quickly.
The most expensive and most powerful structure available for defense, the SAM Site is capable of destroying incoming aircraft within seconds. It also has a long range, so one or two of these should do a good job of defending your base entirely from air attacks.