Big thanks to Babykim for sharing this with us, developer BadPreacher published an explanation about the penetration mechanic in relationship to the changes for German guns.
Source: World of Warships EU Forum
Let us start with HE. The penetration is computed according to the 1/6 or 1/4 calibre rules, rounding to the nearest whole number. The resulting number is the armour thickness that the HE shell cannot penetrate. For example, for a 152mm HE shell we get approximately 25.334 (152/6), which rounds to 25, meaning that 25mm will not be penetrated, but 24mm or thinner will be. The 1/4 rule in 0.6.6 for German guns applies as follows:
- Main battery: all battleships and cruisers of tiers 4-10,
- Secondaries of 128mm and 150mm caliber: all battleships of tiers 7-10, and cruisers Roon and Graf Spee.
Turning to the AP. The penetration is computed according to the 14.3 rule, without rounding. Divide the gun calibre by 14.3. A bounce cannot occur if the result exceeds the thickness of the armour. The check for penetration accounts for the impact angle (normalization), so that the normalized line-of-sight thickness* of amour applies. Consequently, even if the shell did not bounce it may fail to penetrate the armour.
For those who aren’t aware, German guns suffered some changes with Update 0.6.6:
- 150mm HE shell penetration is increased from 25 to 38.
- 203mm HE shell penetration is increased from 34 to 51.
- 210mm HE shell penetration is increased from 35 to 53.
- Nurnberg’s 2nd and 3rd turrets can now rotate 360°.
- Hindenburg is now completely immune to HE splash detonation.