German Rheinmetall-Borsig evaluation tests on a captured 1-K, during 1941, gave a maximum penetration of up to 42 mm of perpendicular rolled homogenous armour plate at 100 metres with APHE and up to 61 mm of perpendicular hardened carbon steel armour plate at 100 metres with APHE. (Note that all tank-building nations had abandoned the use of carburized hardened carbon steel in favour of the increased protection offered by rolled nickel-chromium homogeneous steel armour plate, cast nickel-chromium steel and cast ferro-nickel based armoured alloys by the mid-1920s onwards).