Every vehicle in the game consists of a set of polygons (planes). Collision Model (CM), which is used to calculate the vehicle damage, corresponds exactly to the vehicle model that you see on the screen, but with some simplifications. CM planes, which in reality would be the vehicle armour, are collected into groups. These groups are called "armour groups," and inside of all these groups there is a single armour parameter. In terms of the game model, each "armour group" is a single object.
The game CM has been changed twice already. During the closed beta testing CM had consisted of two "boxes" (hull and turret) with no internal structure (critical damages to internal modules had been purely coincidental). Beginning with the open beta test, CM became more realistic, duplicating vehicle shapes and its internal structure. There were 8 "armour groups" back then.
And now we are introducing 16 armour groups. CM is much more complex and has become more detailed, with all hatches, hinges, ledges and holes as in real tanks. If you study the armour structure of real tanks, you will find that armour in the game has been enhanced and ‘weak’ zones are practically the same as in reality.
