The Panzer II has hidden armor plates behind the normal ones. This means that the Pz.II has 34.5mm Frontal armor in the Hull instead of 20mm and 29mm-34.5mm on the Turret Front
WW2 Soviet Vehicles in Foreign Service Archives - Tank Encyclopedia
Tank Archives
WW2 Soviet Vehicles in Foreign Service Archives - Tank Encyclopedia
Tank Archives
Comparison of armor-piercing - Subcaliber Armor
Comparison of armor-piercing - Subcaliber Armor
WW2
Steam コミュニティ :: ガイド :: Complete Tankery Guide (v1.61)
Panzer III vs T-34, Pzgr 39