An AT weapon which actually saw action in WW2 is the Type 3 AT grenade which had a shaped charge explosive inside. Because the Japanese manufacturing infrastructure was heavily damaged by Allied bombing it was a very simplistic design using expendable materials like wood and cloth. Three different versions existed which differed in the used explosive charge.
The model in FHSW is the Type B with a maximum penetration power of 70 mm. You use it similar to the Soviet RPG-43, in that you sneak up on your target and throw the grenade on it. Of course you should aim for the weaker parts like the rear armor to maximize the damage.