I did a test to see if really thick armor really works: a derp battleship with nothing but armor! Armored with a 1,500mm thick belt AND extended belt, against 10 Battleships, at 2,000 meters.
I am quite confused because the battle log indicates: "belt/extended belt partial pen, X damage", and I wonder how guns with 1,000mm pen at point blank can "partially penetrate" and cause damage through a 1,500mm thick belt.
But there are other times where it simply says "blocked" and deal no damage, which is what I would have expected to happen at all times.
So, how do partial pens work?