I’m not the only person who noticed this but most hull and rear coaxial MGs(and, for the M2 medium tank, the roof MGs) are unmodelled or unoperational. This is a problem on M4s, T-28s, the M2 medium tank, T-34s, Panzer IIIs, Panzer IVs, Panzer Vs, Panzer IVs, Chi-Has, M13/40s KV-1 and 2s, IS-2s, M26s etc.
All of these actually have MGs on that location, and i really wonder why they are not modelled.
Long story short : according to gaijin they are a bit pointless since you can’t shoot planes because of their limited arcs. (And you can’t use them in their primary role : shooting infantry since there is none)
The rule of thumb is that, if the vehicle has a coaxial MG, that’s the one that will work. If it just has a hull MG, then that’ll also work. So it has both, it’s just the coaxial that works.
There are some exceptions but this is how Gaijin likes to do it, and it really doesn’t matter half the time because you still get an MG.
Which makes sense, given the amount of work that would have to be done to rectify this, but I still find it frustrating that a vehicle can have a glaring weak point that does not even function as it should, so you get none of the benefits of an extra machine gun, and all of the downsides. Besides, with a functional (or at very least, modeled) machine gun, you do have a chunk of metal (the receiver of an M1919 is decently thick in real life, even though the game models them and the M2 Browning as only 5mm thick, no matter if you are shooting the barrel into the rest of the gun…) that can sometimes minimize a bit of the damage received if you are shot in the machine gun port.