The overmatch mechanic in the game is not something that new or even more seasoned players often think about or even know about when they are in game. It is the first ‘check’ that is made when you shoot at another ship (or they shoot at you) to determine whether or not your shells will penetrate. That’s why it’s actually good to know about and consider when positioning your ship for a head to head battle.
Overmatch is the term that is used to describe the relative ratio of a shells caliber to the armor it will come into contact with. That ratio is 14.3:1. That means, if the shell is 14.3 or more times greater than the thickness of the armor, regardless of angle, it will penetrate. For low tier ships this is not too important to know about as the bow-in game play is not as relevant due to inexperience and armor tends to be so thin, most cruisers can overmatch other cruisers. At mid to high tiers, however, (tier 5+) players start to learn the advantages of being bow in from more experienced players on their team. This is also where there are far more distinct lines between ship armor thickness and gun caliber.
Most cruisers after tier 5 have bow armor that exceeds 13mm, meaning that with few exceptions only battleships can overmatch their bows and not other cruisers as most cruisers between tier 5-7 are boasting 152mm guns; 13mm is overmatched by 186+mm guns. As you progress down the cruiser lines your bow armor will get thicker, usually from 13mm to 16mm and typically topping out at 25mm at tier 8.
Battleships on the other hand, have bow armor at about 19mm at tier 5 and typically top out at 32mm at tier 8. Of course there are exceptions to this, such as the German BB’s who tend to have this thickest bow armor with plating. The thickest is actually the tier 5 Konig with 150mm plating on its bow. Though there are areas of the bow with 19mm, the majority of the bow, specifically providing cover for the citadel, is 150mm. This means that a tier 5 battleship can actually bow tank every ship in the game under most scenarios. Further, due to the larger caliber of guns on battleships, and heavier armor overall, there is more of a propensity so go bow in against another battleship. This is where the overmatch mechanic is really worth understanding. The only 2 ships, per WarGaming’s design, that are capable of overmatching the bow of (nearly) every ship are the Yamato and Mushashi with their 460mm guns; the largest guns in the game. Therefore, going bow in against them is ill advised. The only ships that are theoretically able to go bow in against them are the Kurfurst and the Frederick der Grosse as they have 60mm plating on their bows. Though there are places where the armor is only 32mm, the thickness that 460mm guns can overmatch, much like the Konig, this plating will prevent frontal citadels under most circumstances.
Both cruisers and battleships are capable of bow tanking ships of the same type and tier. Knowing who can you go face to face with can be critical in certain battles, especially in competitive play. Once again, this is a particularly common tactic among battleships but cruisers can do it as well. For those that wish to know if you can be overmatched or overmatch a certain ship simply divide the ships gun caliber by 14.3. If your armor thickness is greater than that, you’re good, if not, find another tactic. Similarly, you can multiply your armor thickness by 14.3 to find out the minimum caliber of gun required to overmatch your bow. Finally, if you don’t know any of this info or just don’t want to worry about doing the math, I’ve created a Google Sheet than can do the calculations for you or you can look up the ships by name. A disclaimer for this calculator though is I have not included clone ships, such as any of the ARP ships, which are clones of the Myoko and the Kongo. You can find the link below. If you have any trouble with it, find errors, or have some suggestions for improvement, please let me know.