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Lyon 340 MM Ap pen

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609 posts
15,679 battles


how can i calculate the armor thickness of an AP shell can penetrate ?


i just had a game on Lyon facing Saint-Louis she charged me bow in . i couldn't pen her bow !!! tried many times !!!

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Beta Tester
4,603 posts
7,488 battles

The problem in your example is not the penetration capacity by itself but the game mechanics regarding AP ammunition:


AP ammunition can bounce off armor plates, depending in the impact angle:


For the Lyon (as for most ships) if the shell hits at an angle of 45° it has a small chance of bouncing and doing no damage.

This chance increases and becomes 100% chance to bounce (autobounce) at 61° impact angle.

Exception is here if you overmatch. This means that your caliber is simply too big to bounce.  

Overmatch rule is caliber /14.3. So this would be 340/14.3= 23.78 mm of armor that you can overmatch and the angle here is irrelevant.


St Louis has a 25mm bow, so you cannot overmatch it, hence you probably bounced a lot of shells.




There is a pretty good video covering these thematics:





If you just want to know the pen capacity here is a site that has penetration curves:



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Quality Poster
2,263 posts
7,057 battles

I think it's not a problem of penetration but a matter of overmatch.


AP can ignore armor whose thickness is less than caliber/14.3. Saint Louis has 25 mm on its bow so it's an automatic bounce for 340 mm shells.

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