Zoom on vehicles (Battlefield 2)

Guys, for some reason I can't set the zoom function on equipment, for example, on tanks. I understand that if a zoom is installed on the tank, the machine gun will stop working. But even so, nothing came of it. Probably something I missed to register yet. But I would like to install the zoom separately, and not instead of something. For example, assign the middle mouse button to it. Tell me how to do all this, at least replacing something.