Autoaiming Turret Cannon?

Take a look at this post:

http://answers.unity3d.com/questions/388185/make-the-turret-automatically-rotate-to-look-at-wh.html

Some changes need to be made if the gun is not at 0 on the Y axis. Plus, when shooting something, the ball is impacted by gravity, so the ball will drop with respect to the target.

if you want it only to rotate on Z and X axis try something like this:

 Vector3 cannonOrientationVector;
 
 void Update()
 {
 
 cannonOrientationVector = new Vector3(playerObject.transform.position.x, this.transform.position.y, playerObject.transform.position.z);
 
 this.transform.LookAt(enemyOrientationVector);
 
 }

That should work just fine if attached to your cannon script, and if you have the playerObject gameObject available for the cannon script.

Oh, also make sure your cannon starts with a transform.position.y of 0, and cannot be altered anywhere else in the script;