CAMD RF 38-11355-14
The first column is the caliber of the AA gun, second is the thickness of the armour in question, third is the angle of the armour, fourth and sixth are the quality of the armour for penetration and nonpenetration, respectively. Columns five and seven contain the speed at which the penetration or nonpenetration would occur. The last column indicates the type of the armour: the armour is homogeneous in all cases except 2-5, where it is surface hardened with high frequency current.
The conclusions are as follows: "In order to protect the tank from the 105 mm AP shell at all distances, it is necessary to have 130 mm of armour minimum, with high hardness (2.8-3.2) or surface hardened with high frequency current. Even under these conditions, the armour will be breached when hit at 800 m/s at normal."