Wow How did miss cannons....not sure how I missed that.
Lets just hope that those cannons miss you too
Former tank gunner here. Can confirm.
Served with the very first generations of the M1 way back when rocks were soft and Cold Warriors and other dinosaurs proudly walked the Earth...
In any event, I would rule that Vehicle Gunner [in the case of machine guns] would
not stack with other heavy weapon specialties. Vehicle gunner implies that you have some training at shooting while the vehicle is moving... it won't completely get rid of the disadvantages, but it helps. Machine-gunner is more for the infantry role, especially with a braced and still weapon.