How often did tanks have MG's mounted on top of the turret?

As tanks in CoH2 can mostly be upgraded eith an additional MG mounted on the turret I wanted to ask how likely it was in the actual war.

Almost all of the german tanks in the late war, due to air control being lost, they mounted a lot of mg on top

As for american doctrines, i don't really know

In iraq US didn't have any threat of enemy aviation but Abrams had 2 and sometime even three mounted MG on top. Guess why

I thought the idea is to cram as much MG on your tank as possible ala Fury to fend off inf, trucks and aircraft.

all tanks in real life have at least one top-mounted MG (normally for the loader). US tanks have a second MG for the commander... plus the coax.

MGs are not typically for anti-air (waste of ammo), but rather for close-in defense, especially when working with friendly infantry. coh2 is really good at ignoring friendly fire. you don't want to be anywhere near (i.e. within 200 meters) of the front arc of a tank when the main gun goes off.

Not so, in the period at any rate; top MG's are there specifically for AA. Tanks had hull, sponson and coax MG's for anti-inf since WWI, but in WW2 it became apparent that they were vulnerable to fighter bombers and the top MG's were the answer. It's not a waste of ammo; hitting air targets is always hard, but the deterrent effect alone is worth it. A platoon of tanks firing at an incoming strike fighter offers a genuinely respectable threat, which if nothing else makes them less likely to correctly line up a rocket shot or dive bomb.

It mostly depended of the intitial project of the tank. If it had enough mgs mounted on the turret and armour it generally didn't need an mg on top, the problem was though that every mg mounted on the hull is a weak spot that is easier to penetrate. Thats why you will not find any of these in post ww2 tanks.

So its generally better to put less mgs in hull and turret. On the turret the only good spot is the coaxial one near the gun. That gives one, or two mgs on every non light tank where armour really matters and this is way less than tank needs to defend against infantry up close, near the range of throwing an AT granade. It is worth noting that one penetrating AT granade blows up whole tank and kills all crewmembers so it's really impotant to protect against it.

Thats why in all well designed medium and heavy tanks, that didn't have weak spots on armor they added additional mg on the top of turret or even more than one. This gave the tank ability to defend in 2, or in case of hull mouned mg 3 directions instead just one coaxial. It was also much easier to aim becouse you didn't have to move whole turret like in case of coaxial, or tank in case of hill mg. The only problem is exposure of crew member but this is the problem of all mg nests. If mg shoots first, it can suppress infantry and they won't be able to shoot the gunner.

After the war the additional reasoning for putting 2 or even 3 top mgs was the ability to fight helicopters more easily. The main reason still is fighting infantry. Israeli merkava tanks even have mortar mounted on the top of tank.