I’m remaking this topic from the old forum, since these questions I have still hold up.
I’ll start with the turret, specifically the mantlet.
All documents I’ve seen state either an 8 inch basis (effective) thickness or a 4.5 inch actual thickness.
But in WarThunder the M26 has 6 inches of mantlet thickness (152.4 mm). Where does this value come from? Was it actually measured on a tank?
M26 mantlet armor
Additionally there’s a spall shield behind the mantlet which is 1 inch (25.4 mm) thick.
I do know that the mantlet armor used to be 114 mm thick, in line with the actual thickness value, backed up with a 12.7 mm spall shield, which then got changed to an 88.9 mm spall shield in order to reach the 203.2 mm basis thickness.
Next, the hull, specifically on the MG port.
The upper glacis plate of the M26 is meant to provide 6.9 inches (175.26 mm) of basis armor. Basis means that it has an estimated protection equivalent to that of a 6.9 inch flat plate of armor, as US basis armor curve takes into account denormalization of the projectile. You can see the US basis armor curve below.
Following this curve, we can see that the upper glacis plate (4 inches, or 101.6 mm, at 46°) achieves that 6.9 inch basis, as a 46° angle provides a multiplier of around 1.7 (more precisely 1.7208 according to this axis history forum post).
This is also why the ventilator bulge on the M26 is thicker, as due to being at a much lower angle, a higher thickness is required to achieve the same protection.
My question comes from the fact that the machinegun port has the same thickness all over compared to the upper glacis plate, despite being much flatter or much more angled depending on where you hit. Adding to this, the M47 is directly based on the M46, which itself is based on the M26, and the MG port has different thickness depending on where you hit, being 170 mm at it’s flattest (except for the hole made for the MG) and 75 mm on the more angled areas.
M26 and M47 machinegun port
As stated, the M26 machinegun port is 101.6 mm all around, in part because it is just modeled as being part of the upper glacis plate.
Meanwhile the M47, which is indirectly based on the M26, has different thicknesses on the machinegun port depending on the area that is hit.
That’s all. I’d highly appreciate if someone could provide answers for these questions I have, as I’ve tried to search for them myself but so far have come up empty handed.