Modern fighting vehicles have a seperate engine to turn their turrets.
This was one of the first thigns ACE fixed in Arma II.
Turning the turret shouldnt require the engine to run. At least not in such sohisticated vehicles as the Marshall.
This becomes an issue since a turned on engine will increase your heat signature significantally (nice btw).
But because of this a proper support engine for the turret is required.
Greetings