I think what you may be seeing is the following tactic. It can be used with or without the ctrl key. Rapidly and continually press on one of the arrow keys on the keyboard so your turret is spinning around in a circle. And at the same time rapidly left click the mouse with the pointer as near to base of the tank as possible. So you your telling the tank to move in a tight circle. What the other player see's is your tank wobbling in a wierd and confusing way. Once you sense that your opponent is confused, break away in a strait line and take him out. The downside to this tactic is that you have to turn your back on your opponent, but worse, although your tanks moving like crazie you're not actually going anywhere an experienced player will see what you're doing and fire strait at you with no lead. I don't recommend useing this tactic because it's only effective against newbie's and because if it go's wrong you end up looking stupid. I think maybe the not seeing the turret go round is like what virus said a lag issue,but I'm not shure.
