Turrets

Turrets are a defense-only unit — the defensive counterpart to jets. They have a defense of 2 and an offense of 0, which is about twice as strong on defense as a trooper.

Turrets add to your defense against every kind of attacking unit. Nothing stops a missile fired by a baron on your own planet, whether it is nuclear, chemical or biological.

A nuclear missile from another planet is different: a large turret force can bring it down. The more turrets you hold for each region, the more often such a missile fails.

Covert operations on your own planet cannot destroy your turrets. An S3-Sabre from another planet can, and so can a pirate raid.

Some strategy guides call this unit a "Missile Base." It is the same defensive unit.

Build turrets to defend your regions, and pair them with troopers and tanks so you can both defend and attack.